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Different from classical semiconductor photovoltaic devices, for ferroelectric photovoltaic devices, the open-circuit voltage (Voc) can be four and even more orders of magnitude larger than the band gap of the ferroelectric, and the built-in electric field arising from the remnant polarization of the ferroelectric is throughout the bulk region, which is good for obtaining giant power conversion efficiency. Among ferroelectric materials, BiFeO3 with remnant polarization of as high as-100 μC/cm 2 has the narrowest direct band gap (-2.7 eV). These indicate that high power conversion efficiency may be obtained in BiFeO3-based photovoltaic devices. Also, some significant research results about photovoltaic effects of BiFeO3 materials have been recently acquired. In order to better promote the development of BiFeO3-based photovoltaic devices, in this paper, we present a comprehensive review on the latest research progress in photovoltaic effects of BiFeO3 materials with different kinds of topography, including bulk, thin film, and nanomaterials.

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Inorganic perovskite [KNbO3]0.9[BaNi0.5Nb0.5O3‐σ]0.1 (KBNNO) ferroelectric thin films with narrow band gap (1.83 eV) and high room‐temperature remnant polarization (Pr = 0.54 μC/cm2) was grown successfully on the Pt(111)/Ti/SiO2/Si(100) substrates by pulsed laser deposition. Ferroelectric solar cells with a basic structure of ITO/KBNNO/Pt were further prepared based on these thin films, which exhibited obvious external‐poling dependent photovoltaic effects. When the devices were negatively poled, the short‐circuit current and open‐circuit voltage were both significantly higher than those of the devices poled positively. This is attributed to enhanced charge separation under the depolarization field induced by the negative poling, which is superimposed with the built‐in field induced by the Schottky barriers at the interfaces between KBNNO and the two electrodes. When a poling voltage of ‐1 V was applied, the device showed a short‐circuit current as high as 27.3 μA/cm2, which was by two orders of magnitude larger than that of the KBNNO thick‐film (20 μm) devices reported previously. This work may inspire further exploration for lead‐free inorganic perovskite ferroelectric photovoltaic devices.

Developing low-cost, durable, and highly catalytic counter electrode (CE) materials based on earth-abundant elements is essential for dye-sensitized solar cells (DSSCs). In this study, we report a highly active nanostructured compositional material, TiOPC, which contains titanium, oxygen, phosphorus, and carbon, for efficient CE in I/I electrolyte. The TiOPC nanocomposites are prepared from carbon thermal transformation of TiPO in an atmosphere of nitrogen at high temperature, and their catalytic performance is regulated by changing the carbon content in the nanocomposites. The TiOPC with appropriate 24.6 wt % carbon and porous structure exhibits an enhanced electrocatalytic activity in the reduction of I, providing a short-circuit current density of 16.64 mA cm, an open-circuit potential of 0.78 V, and an energy conversion efficiency of 8.65%. The photovoltaic performance of TiOPC CE-based DSSC is even superior to that of a Pt CE-based cell (13.80 mA cm, 0.79 V, and 6.66%). The enhanced catalytic activity of TiOPC is attributed to the presence of predominant Ti-O-P-C structure along with the continuous conductive carbon network and the porous structure.