  The shift current effect, in materials lacking inversion symmetry, may
potentially allow the performance of photovoltaics to surpass the
Shockley-Queisser limit for traditional p-n junction-based photovoltaics.
Although the shift-current effect has been studied from first-principles via
second-order perturbation theory, an understanding of the dynamics of hot
carriers is still lacking. We investigate the dynamics of the shift current in
monolayer WS$_{2}$ via real-time propagation time-dependent density functional
theory (rt-TDDFT). We find that the shift current can be generated within 10 -
20 fs after turning on the lights and dissipates within approximately a few
tens of femtoseconds after turning off the lights. This property can be used
for ultrafast photon detection. This work provides an important step toward
understanding the dynamics of shift-current effects, which is crucial for
device applications.
