Elucidating the Effect of Ferroelectricity in Bismuth Ferrite Solar Cells

To investigate the photoresponse of metal-ferroelectric-metal (MFM) devices, we sandwich polycrystalline bismuth ferrite between two electrodes of similar work function. We use calcium-substitution on the A-site to tailor the properties of bismuth ferrite Bi$_{1-x}$Ca$_x$FeO$_{3-δ}$ from ferroelectric (x < 0.2) to nonferroelectric (x > 0.2). Devices with nonferroelectric Bi$_{1-x}$Ca$_x$FeO$_{3-δ}$ show symmetric current density-voltage (J–V) curves and no photoresponse, resembling their symmetric electronic properties that originate from two opposing Schottky junctions at the symmetric electrodes. In contrast, the J–V curves of ferroelectric Bi$_{1-x}$Ca$_x$FeO$_{3-δ}$ are governed by the polarization direction, introducing directionality through modification of the Schottky barriers. Under illumination, the polarization induced modulation of the Schottky barriers promotes directionality of the photogenerated charge carriers and leverages enhanced photocurrents.