  Despite their potential to exceed the theoretical Shockley-Queisser limit,
ferroelectric photovoltaics (FPVs) have performed inefficiently due to their
extremely low photocurrents. Incorporating Bi2FeCrO6 (BFCO) as the light
absorber in FPVs has recently led to impressively high and record photocurrents
[Nechache et al. Nature Photon. 2015, 9, 61], reviving the FPV field. However,
our understanding of this remarkable phenomenon is far from satisfactory. Here,
we use first-principles calculations to determine that such excellent
performance mainly lies in the efficient separation of electron-hole (e-h)
pairs. We show that photoexcited electrons and holes in BFCO are spatially
separated on the Fe and Cr sites, respectively. This separation is much more
pronounced in disordered BFCO phases, which show exceptional PV responses. We
further set out to design a strategy for next-generation FPVs, not limited to
BFCO, by exploring 44 additional Bi-based double-perovskite oxides. We suggest
9 novel active-layer materials that can offer strong e-h separations and a
desired band gap energy for application in FPVs. Our work indicates that charge
separation is the most important issue to be addressed for FPVs to compete with
conventional devices.
