The Effectof Charge Carrier Cooling on the UltrafastCarrier 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.