Above-Band-Gap Voltage from Oriented Bismuth Ferrite Ceramic Photovoltaic Cells

An open-circuit voltage of 6.9 V was received on oriented ceramic bismuth ferrite (BFO) thin-film solar cells working in an “out-of-plane” mode. The above-band-gap voltage is strongly related to the crystallinity, orientation, and thickness of the BFO film contributing to the bulk photovoltaic effects, which have been further verified by powder X-ray diffraction, scanning electron microscopy, and atomic force microscopy results. The current density–voltage traces show the highest open-circuit voltage of 6.9 V on 600 nm thick cells heated at 500 °C. Polings along the opposite directions would modify the current density–voltage traces accordingly, which suggests the ferroelectric nature of the solar cells.