  We study a simple model of photovoltaic energy harvesting across a Mott
insulating gap consisting of a correlated layer connected to two metallic leads
held at different chemical potentials. Upon driving the layer with a time
periodic electric field a particle current is induced from the low-energy to
the high-energy lead. We address in particular the issue of impact ionization,
whereby a particle photoexcited to the high-energy part of the upper Hubbard
band uses its extra energy to produce a second particle-hole excitation. We
find a drastic increase of the photocurrent upon entering the frequency regime
where impact ionization is possible. At large values of the Mott gap, where
impact ionization is energetically not allowed, we observe a suppression of the
current and a piling up of charge in the high-energy part of the upper Hubbard
band. Our study is based on a Floquet-DMFT treatment with the so-called
auxiliary master equation approach as impurity solver. We verify that an
approximation, whereby the self-energy is taken diagonal in the Floquet
indices, is appropriate for the parameter range we are considering.
