Time-Resolved Infrared Spectroscopy Directly Probes Free and Trapped Carriers in Organo-Halide Perovskites

Free carrier dynamics in organo-halide perovskites can directly reveal information about their carrier lifetimes and indirectly reveal information about trap state distributions, both of which are critical to improving their performance and stability. Time-resolved photoluminescence (TRPL) spectroscopy is commonly used to probe carrier dynamics in these materials, but the technique is only sensitive to radiative decay pathways and may not reveal the true carrier dynamics. We used time-resolved infrared (TRIR) spectroscopy in comparison to TRPL to show that photogenerated charges relax into free carrier states with lower radiative recombination probabilities, which complicates TRPL measurements. Furthermore, we showed that trapped carriers exhibit distinct mid-infrared absorptions that can be uniquely probed using TRIR spectroscopy. We used the technique to demonstrate the first simultaneous measurements of trapped and free carriers in organo-halide perovskites, which opens new opportunities to clarify how charge trapping and surface passivation influence the optoelectronic properties of these materials.