Visualizing Carrier Diffusion in Cs‐Doping FAPbI₃ Perovskite Thin Films Using Transient Absorption Microscopy

Abstract The determination of the semiconducting materials performance heavily relies on the diffusion coefficient and length of the carrier. Recently, significant progress is made in enhancing solar cell efficiency through improved carrier diffusion in perovskite thin films. However, the spatial‐temporal mechanisms underlying carrier transport remain unclear. Recent advancements in utilizing transient absorption microscopy (TAM) offer promising opportunities to directly visualize the carrier transport dynamics within perovskite films. Here, the wide‐field imaging TAM combined with X‐ray diffraction and scanning electron microscopy is employed to investigate the spatial‐temporal carrier transport dynamics in FA_1−xCs_xPbI₃ perovskites with varying Cs doping ratios. The experimental results indicate that the diffusion constant remains consistent regardless of the excitation power. Moreover, a decrease in the Cs doping ratio leads to an increase in the diffusion length within FA_1−xCs_xPbI₃ perovskites. The measurements reveal a highest diffusion coefficient of up to 0.085 cm² s⁻¹ and a maximum diffusion length of ≈1.4 µm in FA_0.97Cs_0.03PbI₃. Comparative analysis of short‐circuit current density, open‐circuit voltage, fill factor, and power conversion efficiency demonstrates that FA_0.97Cs_0.03PbI₃ exhibits superior device efficiency. The TAM visualizes spatial/ temporal carrier diffusion dynamics, showing a significant correlation with device efficiency and thus providing valuable insights for further enhancing device performance.