Visible-light photovoltaic effect in high-temperature ferroelectric BaFe₄O₇

Ferroelectric photovoltaics, as a new type of solar cell, relying on an internal electric field instead of p-n or Schottky junctions, can considerably improve the efficiency of charge separation and migration. But, non-volatile elements containing ferroelectrics with narrow bandgaps and excellent photoelectric performances are still scarce. Herein, a new ferroelectric compound, BaFe4O7, has been synthesized by a conventional hydrothermal method. A polar trigonal structure (P31c) was proposed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. UV-vis-NIR diffuse reflectance spectrum revealed a visible-light bandgap Eg of 2.18 eV. Intrinsic ferroelectricity with a high Curie temperature (Tc ∼ 791 K) was confirmed by dielectric and ferroelectric measurements. The electrical saturation polarization (Ps), remanent polarization (Pr) and coercive field (Ec) were determined as 6.34 μC cm-2, 3.32 μC cm-2 and 42.38 kV cm-1 respectively. A bulk photovoltaic effect was observed in the poled sample with a steady-state photocurrent of 39 nA cm-2 and photovoltage of 0.19 V under standard AM 1.5G illumination, which demonstrated its promising applications in photoelectric devices.