Ultrafast transient infrared spectroscopy for probing trapping states in hybrid perovskite films

Halide-based perovskite films are popular absorber materials used in solar cells, but undesired effects such as charge recombination and trapping continue to cap record conversion efficiencies. Here, the authors use femtosecond transient mid-infrared spectroscopy to elucidate electron recombination and trapping in the conduction bands of various compositions of perovskite thin films. Studying the charge dynamics of perovskite materials is a crucial step to understand the outstanding performance of these materials in various fields. Herein, we utilize transient absorption in the mid-infrared region, where solely electron signatures in the conduction bands are monitored without external contributions from other dynamical species. Within the measured range of 4000 nm to 6000 nm (2500-1666 cm(-1)), the recombination and the trapping processes of the excited carriers could be easily monitored. Moreover, we reveal that within this spectral region the trapping process could be distinguished from recombination process, in which the iodide-based films show more tendencies to trap the excited electrons in comparison to the bromide-based derivatives. The trapping process was assigned due to the emission released in the mid-infrared region, while the traditional band-gap recombination process did not show such process. Various parameters have been tested such as film composition, excitation dependence and the probing wavelength. This study opens new frontiers for the transient mid-infrared absorption to assign the trapping process in perovskite films both qualitatively and quantitatively, along with the potential applications of perovskite films in the mid-IR region.

Automated summary

In this study, the authors use femtosecond transient mid-infrared spectroscopy to investigate electron recombination and trapping in various compositions of perovskite films. They find that iodide-based films have a higher tendency to trap excited electrons compared to bromide-based derivatives. This research provides important experimental data for understanding the performance of perovskite materials.