Robust and reversible polar topological center domains were found in BiFeO3 nanodots, which are individually controllable.

Achieving high power conversion efficiencies (PCEs) in ferroelectric photovoltaics (PVs) is a longstanding challenge. Although recently ferroelectric thick films, composite films, and bulk crystals have all been demonstrated to exhibit PCEs >1%, these systems still suffer from severe recombination because of the fundamentally low conductivities of ferroelectrics. Further improvement of PCEs may therefore rely on thickness reduction if the reduced recombination could overcompensate for the loss in light absorption. Here, a PCE of up to 2.49% (under 365-nm ultraviolet illumination) was demonstrated in a 12-nm Pb(Zr 0.2 Ti 0.8)O 3 (PZT) ultrathin film. The strategy to realize such a high PCE consists of reducing the film thickness to be comparable with the depletion width, which can simultaneously suppress recombination and lower the series resistance. The basis of our strategy lies in the fact that the PV effect originates from the interfacial Schottky barriers, which is revealed by measuring and modeling the thickness-dependent PV characteristics. In addition, the Schottky barrier parameters (particularly the depletion width) are evaluated by investigating the thickness-dependent ferroelectric, dielectric and conduction properties. Our study therefore provides an effective strategy to obtain high-efficiency ferroelectric PVs and demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices.

In this work, the observations of different resistive switching polarities of epitaxial BaTiO3 (BTO) thin films fabricated by pulsed laser deposition are reported. The BTO films with various ferroelectric states and oxygen vacancy (VO) concentrations are achieved by carefully controlling the oxygen pressure during the depositions. For films with no ferroelectricity and high VO concentrations, the resistance will change from a low resistance state (LRS) to a high resistance state (HRS) during a positive voltage cycle (0 → 3 → 0 V), and from a HRS to a LRS during a negative voltage cycle (0 → −3 → 0 V). However, completely opposite RS polarity is observed for the films with weak ferroelectricity and intermediate VO concentrations. Such RS behaviors and polarity can be hardly observed or negligible for the films with good ferroelectricity and nearly free of VO. It is proposed that the unique resistance switching polarities of BTO films are attributed to the competition between the ferroelectricity and oxygen vacancy migration dynamics. Results clarify the complex RS mechanisms in the BTO films, and address the competing ferroelectricity and VO migration in modulating the RS behaviors of ferroelectric oxide‐based resistive memory devices.

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A unified mechanism for the colossal electroresistance effects in Nb:SrTiO3-based heterojunctions is revealed.