Origin of lowered bandgap in Bi2FeCrO6 with alternate stacking of B-site cations by first-principles investigations

A lowered bandgap of ferroelectric photovoltaic (FE-PV) materials is exceedingly important for achieving practical FE-PV technology. The bandgap tailoring of pseudo-cubic Bi2FeCrO6 (p-BFCO) with different magnetic orderings was investigated using first-principles calculations. Results show that A-type antiferromagnetic ordering and ferromagnetic (FM) ordering of p-BFCO have a narrowed bandgap (1.12 eV), indicating that p-BFCO is sensitive to its magnetic ordering. Electronic structure analysis shows that the narrowed bandgap of A-type and FM orderings originate from the downward shift of Fe 3d antibonding states due to the ionicity strengthening of Fe. The polarization of p-BFCO maintains a sufficient size for different magnetic orderings. The bandgap of the C-type ordering is the most stable structure, which can be modulated from 2.167 to 1.206 eV by strain based on different substrates, originating from the Bi 6p and Fe 3d antibonding states moving toward the Fermi energy. Meanwhile, the polarization of pc-BFCO becomes large with increasing strain due to the relative displacement of cations and anions. This work provides an alternative way to lower the bandgap of FE-PV materials.