Bismuth ferrite sensitization of nanostructured titanium dioxide and/or zinc oxide-based for photovoltaic device applications

Bismuth ferrite (BFO) is a ‘mid-range’ band gap, multiferroic (ferroelectric, antiferromagnetic) material of interest in numerous applications39,96,100-106. Though its use in photovoltaic applications has been investigated39,96,100-102,104,105 with interesting result, such a material has not yet been used as a photovoltaic sensitizer/thin absorber in sensitized solar cell (SSC) or extremely thin absorber solar cell (eta-SC) devices. A band gap (Eg~2.2-2.8eV) 40,100,103,105,117,139,147 within the visible light range (albeit high) makes BFO a potential candidate for such application. Moreover, BFO is ferroelectric (Ec ~500-600kV/cm, Pr = 60μC/cm2)100,159, which provides the material with an internal electric field (which can be directed/’poled’ towards one electrode or another in a(n) SSC/eta-device), which may provide an additional mechanism for either or both charge separation and transport.CuSCN/ZnO, CuSCN/TiO2, CuSCN/Bi-Fe-Zn-O/ZnO, CuSCN/BFO/TiO2 thin-film ‘sandwich-like’ structures were fabricated on transparent-conducting-oxide-glass (TCO) substrates, via combinations of electrodeposition and suspension or sol-gel (requiring ‘high temperature’ for crystallization) dip-coating, and characterized at various stages of production to assess material/phases present, optical absorbance characteristics, and preliminary electronic device performance. ‘High-temperature’ heat treatments in air or N2 of Bi-Fe-Zn-O/ZnO samples result in films yielding crystalline non-BFO phases, while O2 annealing of similar samples appear promising. BFO has been successfully crystallized on nearly-pure anatase TiO2 synthesized/deposited two ways, as well as on F:SnO2-glass. Moreover, BFO is found to enhance absorbency in at least a portion the visible portion of the electromagnetic spectrum. Such are promising signs that thin-absorber-PV devices based on either TiO2 or ZnO may be viable for development in the near future.M.S., Materials Science and Engineering -- Drexel University, 201

Cryogenic EBSD reveals structure of directionally solidified ice-polymer composite

Despite considerable research efforts on directionally solidified or freeze-cast materials in recent years, little fundamental knowledge has been gained that links model with experiment. In this contribution, the cryogenic characterization of directionally solidified polymer solutions illustrates, how powerful cryo-scanning electron microscopy combined with electron backscatter diffraction is for the structural characterization of ice–polymer composite materials. Under controlled sublimation, the freeze-cast polymer scaffold structure is revealed and imaged with secondary electrons. Electron backscatter diffraction fabric analysis shows that the ice crystals, which template the polymer scaffold and create the lamellar structure, have a-axes oriented parallel to the direction of solidification and the c-axes perpendicular to it. These results indicate the great potential of both cryo-scanning electron microscopy and cryo-electron backscatter diffraction in gaining fundamental knowledge of structure–property–processing correlations. - Highlights: • Cryo-SEM of freeze-cast polymer solution reveals an ice-templated structure. • Cryo-EBSD reveals the ice crystal a-axis to parallel the solidification direction. • The honeycomb-like polymer phase favors columnar ridges only on one side. • Combining cryo-SEM with EBSD links solidification theory with experiment