A-site cation engineering and halide tuning 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 precursor engineering has been employed to investigate its impact on the structural and optical properties of BA(MA )PbX (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 -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.