Comparative Optical Studies and Transient Behavior in Two-Dimensional Organic-Inorganic Hybrid Lead-Iodide Perovskite Films*

We synthesized two-dimensional (2D) organic-inorganic hybrid lead-iodide perovskite films by incorporating butylammonium and phenylethyl ammonium. This was achieved using a two-step chemical vapor deposition process, resulting in high-quality 2D Ruddlesden-Popper-type hybrid halide perovskite films. Subsequently, heterojunctions of these films with a thin SnO₂ layer were also synthesized. This study offers a comparative analysis of the effects of the organic cation and the SnO₂ heterojunctions on the optical properties of the perovskite films. Various optical characterization techniques including absorption, photoluminescence (PL), time-resolved photoluminescence (TRPL), and transient absorption spectroscopy (TAS) employing an ultrafast femtosecond pump-probe technique were utilized. The absorption and PL measurements highlighted characteristic features of the 2D quantum wells in these perovskites. The TRPL analysis revealed the effects of the organic cations and the SnO₂ layer in the PL lifetimes. Furthermore, TAS measurements revealed distinctions in the lifetime and evolution of the transient absorption spectrum between the two perovskite films and their SnO₂ heterojunction counterparts, providing valuable insights into the structural disparities within these perovskites and the underlying factors governing excitonic and carrier dynamics.