The Effect of Charge Carrier Cooling on the Ultrafast Carrier Dynamics in Cs$_2$AgBiBr$_6$ Thin Films

TL;DR

This study links hot carrier cooling to ultrafast mobility loss in Cs$_2$AgBiBr$_6$ thin films, revealing that rapid cooling causes the initial decline in charge carrier mobility crucial for optoelectronic applications.

Contribution

It provides direct experimental evidence connecting hot carrier cooling with ultrafast mobility loss in Cs$_2$AgBiBr$_6$, clarifying a key limitation in its optoelectronic performance.

Findings

Hot carriers cool towards band edges at 0.58 ps$^{-1}$

Cooling rate coincides with mobility loss rate

Establishes a direct link between cooling and mobility loss

Abstract

Cs$_2$AgBiBr$_6$ 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 Cs$_2$AgBiBr$_6$ thin film sample. From transient absorption spectroscopy, we find that hot carriers cool towards 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 timescale.