Bismuth triiodide (BiI3) is a potential candidate for application in solar cell due to its good optoelectronic properties and because it is free of toxic elements. It can be used as the absorber material in solar cells or converted into the perovskite-like material MA3Bi2I9, suitable also for photovoltaic applications. Bismuth triiodide has been prepared by physical vapour transport (PVT) and by solution process through spin coating. In this work we present optical and structural/topological properties of BiI3 deposited by thermal evaporation under high vacuum. The films are slightly tensile, polycrystalline, homogenously distributed and with good adherence on several substrates, with an indirect bandgap of 1.81 eV, index of refraction of 3.3 (630 nm), photoluminescence centered at 1.74 eV and a Raman peak at 118cm-1 associated with the Ag mode.

Methods of obtaining large grain size and high crystallinity in absorber materials play an important role in fabrication of high-performance methylammonium lead iodide (MAPbI3) perovskite solar cells. Here we study the effect of adding small concentrations of Cd2+, Zn2+, and Fe2+salts to the perovskite precursor solution used in the single-step solution fabrication process. Enhanced grain size and crystallinity in MAPbI3 films were obtained by using 0.1% of Cd2+ or Zn2+in the precursor solution. Consequently, solar cells constructed with Cd- and Zn-doped perovskite films show a significant improvement in device performance. These results suggest that the process may be an effective and facile method to fabricate high-efficiency perovskite photovoltaic devices.

The substitutional solid solutions in the Bi(Gd) - Fe - O and Bi(Nd) - Fe - O systems of the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 types with x up to 0.20 were synthesized by the solid-state reaction method and investigated using X-ray diffraction analysis and infrared reflective spectrometry in the wavelength range from 12.5 to 24 μm. It was determined that the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 crystal structure is a distorted form of perovskite, R3c space group. Two extremums at 18.2 μm (strong extremum) and 22.5 μm (rather weak extremum) on the infrared reflection spectra of the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 solid solutions were discovered. The extremum at 18.2 μm corresponds to the Fe – O stretching vibrations and the extremum at 22.5 μm corresponds to the O - Fe – O bending vibrations of the FeO6 groups. The growth of reflectivity of the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 solid solutions in comparison with pure BiFeO3 and the displacement of the reflectivity band maximum into the side of the spectrum with longer wavelengths with the increase of the atomic part of the substitutive element x up to 0.20 were found.

Ternary sulfides and selenides in the distorted-perovskite structure (“chalcogenide perovskites”) are predicted by theory to be semiconductors with band gap in the visible-to-infrared and may be useful for optical, electronic, and energy conversion technologies. Density functional theory can be used in combination with computational thermodynamics to predict the pressure-temperature phase diagrams for chalcogenide perovskites. We report results using the Strongly Constrained and Appropriately Normed (SCAN) and the rVV10 density functionals, and compare to previously-published results using the PBEsol functional. We highlight the windows of thermodynamic equilibrium between solid chalcogenide perovskites and the vapor phase at high temperature and very low pressure. These phase diagrams can guide adsorption-limited growth of ternary chalcogenides by molecular beam epitaxy (MBE).

Application of lead-halide perovskite nanostructures for photovoltaic and light emitting applications depends on fashion of the surface termination. The reasonable choice of surface ligands for perovskite nanostructures prevent formation of trap states and contribute to chemical stability, wide opening of the bandgap, and intensity of absorption and photoluminescence of perovskite nanostructures. This work provides atomistic arguments for dual ligand protocol of surface passivation of fully inorganic perovskite quantum dots with fully organic ligands being a mix of cations (ethyl-ammonium) and anions (acetic) in nearly equal proportions. Computed binding energies of either individual ligands or anion-cation pairs demonstrate high stability in comparison to thermal energy and are concluded to be favourable choice in synthesis of colloidal perovskite quantum dots for light emitting applications.

Semiconductor-based heterojunctions have been shown to be effective photocatalytic materials to overcome the drawbacks of low photocatalytic efficiency that results from a high rate of electron−hole recombination and narrow photo-response range. In this paper, we report on the study of heterojunctions made from visible light active, graphitic carbon nitride, g-C3N4), and UV light active, strontium pyroniobate, Sr2Nb2O7. Heterojunctions made from a combination of g-C3N4 and nitrogen-doped Sr2Nb2O7 obtained at different temperatures were also studied to determine the effect of N doping. The photocatalytic performance was evaluated by using photocatalytic hydrogen evolution reaction (HER)from water g under visible light irradiation. It was found that the photocatalytic activities of as prepared heterojunctions are significantly higher than that of individual components under similar conditions. Heterojunction formed from g-C3N4 and N-doped Sr2Nb2O7 at 700°C (CN/SNON-700) showed better performance than heterojunction made from g-C3N4 and Sr2Nb2O7 (CN/SNO). A plausible mechanism for the heterojunction enhanced photocatalytic activity is proposed based on, relative band positions, and photoluminescence data.

Simple and efficient approach for artificial photosynthesis of CO2 reduction into ethanol with flexible functional multi-layered membrane catalysts is suggested. The g-C3N4 and BiVO4 particle were synthesized by self-condensation and hydrothermal method. g-C3N4 membrane catalyst and g-C3N4/BiVO4 layered membrane catalyst were fabricated by casting and shaping of Nafion polymer mixture. XRD, FT-IR and XPS analyses proved that the intrinsic properties of g-C3N4 and BiVO4 were maintained after fabricating flexible functional multi-layered membrane catalyst. The interfacial contact between g-C3N4 and BiVO4 particles in flexible membrane catalyst for efficient transport of photogenerated electron was revealed by TEM and photoelectrochemical analysis. Finally, photochemical CO2 reduction reaction was performed with flexible functional multi-layered membrane catalysts. The g-C3N4 membrane catalysts produced 147 μM of ethanol during 12 hrs of CO2 reduction reaction while the g-C3N4/BiVO4 layered membrane catalysts produced 256 μM of ethanol during 12 hrs of CO2 reduction reaction. This is due to the higher solar light harvesting and efficient hole-charge separation from functional multi-layered BiVO4 membrane catalyst leading to the higher electron transport rate to g-C3N4 membrane catalysts, promoting the CO2 reduction reaction on the surface of g-C3N4 membrane catalyst.