The Effect of Charge Carrier Cooling on the Ultrafast Carrier Dynamics in Cs₂AgBiBr₆ Thin Films

Cs2AgBiBr6 shows promise for solution-processable optoelectronics, such as photovoltaics, photocatalysis, and X-ray detection. However, various spectroscopic studies report rapid charge carrier mobility loss in the first picosecond after photoexcitation, limiting carrier collection efficiencies. The origin of this rapid mobility loss is still unclear. Here, we directly compare hot excitation with excitation over the indirect fundamental bandgap, using transient absorption and THz spectroscopy on the same Cs2AgBiBr6 thin film sample. From transient absorption spectroscopy, we find that hot carriers cool toward the band-edges with a cooling rate of 0.58 ps–1, which coincides with the observed mobility loss rate from THz spectroscopy. Hence, our study establishes a direct link between the hot carrier cooling and ultrafast mobility loss on the picosecond time scale.