  Two-dimensional quantum spin Hall (QSH) insulators are a promising material
class for spintronic applications based on topologically-protected spin
currents in their edges. Yet, they have not lived up to their technological
potential, as experimental realizations are scarce and limited to cryogenic
temperatures. These constraints have also severely restricted characterization
of their dynamical properties. Here, we report on the electron dynamics of the
novel room-temperature QSH candidate bismuthene after photoexcitation using
time- and angle-resolved photoemission spectroscopy. We map the transiently
occupied conduction band and track the full relaxation pathway of hot
photocarriers. Intriguingly, we observe photocarrier lifetimes much shorter
than in \red{conventional} semiconductors. This is ascribed to the presence of
topological in-gap states already established by local probes. Indeed, we find
spectral signatures consistent with these earlier findings. Demonstration of
the large band gap and the view into photoelectron dynamics mark a critical
step toward optical control of QSH functionalities.
