Identifying the Cascade Carrier Transfer Processes in Quasi-2D Perovskite Films.

Quasi-two-dimensional (2D) perovskites have garnered substantial research interest due to their remarkable stability and exceptional optoelectronic properties. It is well recognized that upon photoexcitation, electrons transfer from phases with narrower quantum well widths (small n) to those with wider ones (large n), ultimately reaching the three-dimensional (3D) phase. However, it remains difficult to distinguish whether charge carriers transfer directly to the 3D perovskite or undergo a cascade transfer through other 2D phases within the first picoseconds after excitation. In this work, we established a straightforward method to distinguish the cascade charge transfer processes by comparing the time resolution fitted from the rising edges of bleaching signals corresponding to different 2D phases. This deconvolution fitting method further enabled calibration of the time zeros on kinetic curves. The corrected results exhibit consistency with those derived from the optical Kerr effect measurements, thereby cross-validating the accuracy of this approach. The experimental results indicate that under low light intensity, no cascade transfer occurs between two different small n phases of the quasi-2D perovskite (BDA)FA3Pb4I13 thin films in the initial picoseconds following photoexcitation. Instead, electrons transfer directly from small n phases to the 3D phase. This work provides a method for identifying cascade carrier transfer processes accurately, potentially providing enhanced guidance and a deeper understanding of optoelectronic materials.