Characterization of Intrinsic Charge Carrier Dynamics in Lead Halide Perovskite Films Using Time-Resolved Terahertz Spectroscopy

The behaviors of free charge carriers and the crucial factor of carrier diffusion length in perovskite films are intricately connected, with both time-resolved terahertz spectroscopy (TRTS) and time-resolved photoluminescence (TRPL) being viable techniques for investigation. Yet, the consistency of the results these two methods provide regarding charge dynamics is still a matter of debate. In this study, we scrutinize the excited-state dynamics within MAPbI3 films, which were fabricated through three distinct methods, under equivalent excitation conditions for both TRTS and TRPL analyses. Our research uncovers that films undergoing two-step annealing with Pb(SCN)2 exhibit extended charge carrier lifetimes and lower rates of both first-order and second-order recombinations benefiting from the improved grain sizes. Across all samples, we note that the decay rates measured by TRPL are consistently faster than those recorded by TRTS. This discrepancy highlights the critical need to separate the behaviors of charge carriers from those of emissive bound states, which is essential for precisely assessing the fundamental dynamics of free charges and the diffusion lengths of carriers in perovskite films.