Effect of Structural Defects and Impurities on the Excited State Dynamics of 2D BA2PbI4 Perovskite

In this work, we show that the quality of the precursor and the thin film preparation strongly affect the optoelectronic properties of the 2D perovskite BA₂PbI₄. 2D perovskites with alkylammonium organic cations such as butylammonium (BA) are relatively soft structures that exhibit large dynamic disorder and phase variations. Here we show, by a variety of spectroscopy techniques (steady state absorption, photoluminescence and ultrafast transient absorption), that at temperatures below the phase transition (253 K) the material exhibits excitonic features from the room temperature phase (due to incomplete structural transition) and a broadband emission at 560–600 nm (due to self-trapped excitons) with varied relative intensities depending on the precursors and processing conditions. This suggests that the processing conditions have a large influence on the crystallization and introduction of extrinsic defect impurities directly affecting the optoelectronic properties. Making absolute statements about the properties of BA₂PbI₄ requires improved control over the materials thin film deposition and a better understanding of the role of the lattice vibrational dynamics and extrinsic defects on the exciton dynamics.