Figure 1
From: New high Tc multiferroics KBiFe2O5 with narrow band gap and promising photovoltaic effect

Selection rules for ferroelectric photovoltaic materials.
(a) Schematic illustration of mechanism for photovoltaic effect in ferroelectric materials. (b) Spectra of solar radiance and UV-Vis-near IR absorption of BiFeO3 and KBiFe2O5. (c) Maximum theoretical efficiency vs. band gap; AM1.5 illumination. (d) Schematic electronic DOS of Fe3+ in octahedral Oh and tetrahedral Td coordination.