The application of ferroelectric materials (i.e. solids that exhibit spontaneous electric polarisation) in solar cells has a long and controversial history. This includes the first observations of the anomalous photovoltaic effect (APE) and the bulk photovoltaic effect (BPE). The recent successful application of inorganic and hybrid perovskite structured materials (e.g. BiFeO3, CsSnI3, CH3NH3PbI3) in solar cells emphasises that polar semiconductors can be used in conventional photovoltaic architectures. We review developments in this field, with a particular emphasis on the materials known to display the APE/BPE (e.g. ZnS, CdTe, SbSI), and the theoretical explanation. Critical analysis is complemented with first-principles calculation of the underlying electronic structure. In addition to discussing the implications of a ferroelectric absorber layer, and the solid state theory of polarisation (Berry phase analysis), design principles and opportunities for high-efficiency ferroelectric photovoltaics are presented.

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Ferroelectric Materials for Solar Energy Conversion: Photoferroics Revisited

A review of flexible perovskite oxide ferroelectric films and their application

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications.

Environmentally friendly BaTiO3 is emerging as a potential photocatalyst due to its tunable electronic structure. Although originally believed to be a poor photocatalyst due to its wide band gap, several strategies have been implemented to reduce its band gap. One such approach is doping, but this often leads to the formation of mid gap recombination centers and diminishes the efficiency of the material. In the present work, we study for the first time the effect of site occupancy of Rh on the electronic structure of BaTiO3. As the theoretical results reveal that if Rh occupies both Ba and Ti sites simultaneously it leads to the formation of mid gap states, an experimental approach is implemented to reduce the band gap of BaTiO3 while simultaneously avoiding the formation of recombination centers. The facile one pot hydrothermal approach reported here directs the Rh towards Ba sites leading to a decrease in the band gap due to the appearance of donor Rh3+ states, suppressing the formation of Rh4+ states. A promising photocatalytic activity of 96% degradation of methylene blue dye in 120 minutes was observed for the 0.5 Rh sample indicating the high efficiency of the material.

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Rhodium doping augments photocatalytic activity of barium titanate: effect of electronic structure engineering

Semiconducting BaTiO3@C core-shell structure for improving piezo-photocatalytic performance

We report on the synthesis of photoferroic Cr3+-doped BaTiO3 nanoparticles with nominal Cr content ranging from 2–8 mol% by a microwave-assisted hydrothermal method. The absorption properties of the doped systems are significantly enhanced due to the d–d band transition of Cr3+/4+. The structural properties of the materials are examined on the basis of lattice distortions given by the tolerance factor and microstrain. Raman scattering provides complementary information on the lattice vibrations indicating a softening of the longitudinal optic (LO) phonon mode located at 716 cm−1 with increasing Cr concentration. The charge transport properties investigated through electrochemical impedance spectroscopy (EIS) demonstrate that there is a reduction in the charge transfer resistance from 5.2 Ω to 4.3 Ω for the undoped and 4 mol% Cr3+-doped respectively, which favors the degradation kinetics. The photo-oxidation ability of the systems is evaluated by time evolution of photodegradation of methyl orange under standardized solar irradiation. The experimental results confirm that the best photocatalytic performance is achieved with the 4 mol% Cr3+-doped BaTiO3 nanoparticles, which is ∼2.7 times higher than for the undoped sample. Evidence of superoxide radical being the dominant active species is provided by in situ reactive oxide species (ROS) capture experiments.

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B-site modified photoferroic Cr3+-doped barium titanate nanoparticles: microwave-assisted hydrothermal synthesis, photocatalytic and electrochemical properties

Ultrafast microwave-assisted hydrothermal synthesis and photocatalytic behaviour of ferroelectric Fe3+-doped BaTiO3 nanoparticles under simulated sunlight

A. Hadj Youssef

Papers

B-site modified photoferroic Cr3+-doped barium titanate nanoparticles: microwave-assisted hydrothermal synthesis, photocatalytic and electrochemical properties

Ultrafast microwave-assisted hydrothermal synthesis and photocatalytic behaviour of ferroelectric Fe3+-doped BaTiO3 nanoparticles under simulated sunlight

Impact of negative oxygen ions on the deposition processes of RF-magnetron sputtered SrTiO3 thin films