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This study comes up with a new architecture of multi-layered photoanode electrodes containing three thick layers (i.e., 4 μm) of nanocrystalline TiO2 particles and three thin layers (i.e., 1 μm) of uniform TiO2 aggregates, which are alternately deposited. The aggregates layers are deposited by a straightforward gel process, developed for the preparation of uniform and sponge-like light scattering layer for dye-sensitized solar cells (DSCs) applications. The aggregates layers are composed of uniform spherical particles with average diameter of 2 μm, containing small nanoparticles with the average grain size of 20 nm. The nanocrystalline layers contain 20-nm-diameter TiO2 nanoparticles. X-ray diffraction (XRD) reveals that the nanocrystalline layers have a pure anatase phase, whereas the aggregates layers show a mixture of anatase and rutile phases. Diffuse reflectance spectroscopy (DRS) demonstrates that the multi-layered electrode enjoys better light scattering ability than that of mono-layered electrode due to the incorporation of a thin light scattering layer into the nanocrystalline film. The multi-layered DSC shows the highest power conversion efficiency of 7.85% as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy (EIS). From IPCE measurement, the external quantum efficiency of the multi-layered cell at 530 nm is equal to 89%, which is higher than that of mono-layered cell (i.e., 78%). © 2015 Elsevier B.V. All rights reserved. Source


Bakhshayesh A.M.,SUN Nanotechnologists Company
Materials Research Bulletin | Year: 2016

This study presents a new double-layered TiO2 film containing a nanocrystalline under-layer and a uniform, sponge-like light scattering over-layer for dye-sensitized solar cells (DSCs) application. The over-layer is composed of 2-μm-diameter uniform aggregates, containing small nanoparticles with the average grain size of 20 nm. X-ray diffraction reveals that the light scattering layer has a mixture of anatase and rutile phases, whereas the nanocrystalline layer has a pure anatase phase. Ultraviolet-visible (UV-vis) spectra show that the light scattering layer has lower band gap energy than the nanocrystalline under-layer, extending the absorption of TiO2 into visible region. Diffuse reflectance spectroscopy demonstrates that the double-layered electrode enjoyed better light scattering ability. The double-layered DSC shows the highest power conversion efficiency of 7.69% and incident photon-to-current efficiency of 88% as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy. © 2015 Elsevier Ltd. All rights reserved. Source


Bakhshayesh A.M.,SUN Nanotechnologists Company
Journal of Solid State Electrochemistry | Year: 2016

This study comes up with the facile preparation of Sr,Zn co-doped TiO2 xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs). The film contains 2.5-μm-diameter spheres assembled from 60 nm nanoparticles. X-ray photoelectron spectroscopy (XPS) shows that Sr2+ and Zn2+ ions to be well incorporated into the TiO2 crystal lattice without forming specific strontium and zinc compositions. The crystallite size, phase composition, and band structure of the spheres depend on the dopants concentration. Isolated energy levels near valence band as a result of the foreign ions introduction improve the photocatalytic activity of the prepared TiO2 spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 0.4 at.% Zn showed the highest power conversion efficiency of 7.87 % and short circuit current density of 18.75 mA cm−2 thanks to lower charge transfer resistance (2.16 Ω cm2), lower electron transit time (1.19 ms), and higher electron diffusion coefficient (18.1 × 104 cm2 S−1) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of the simultaneous introduction of alkaline earth ions and transition ions into TiO2 xerogel films will open up a new insight into the fabrication of high performance DSCs. © 2015, Springer-Verlag Berlin Heidelberg. Source


Bakhshayesh A.M.,SUN Nanotechnologists Company | Bakhshayesh N.,SUN Nanotechnologists Company
Journal of Electroceramics | Year: 2016

In this study, we present the deposition of uniform sponge-like films using a novel niobium-stabilised TiO2 gel for dye-sensitized solar cells (DSCs) applications. The introduction of Nb into TiO2 lattice limits the transformation from anatase to rutile phase, stabilising anatase nanoparticles. The films are composed of uniform spherical particles with diameter around 3 μm, containing small nanoparticles with the average grain size of 40 nm, deposited by dip coating method. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) reveal that Nb5+ is well incorporated into the titania crystal lattice without forming specific niobium phases. UV–Visible spectra show that the doped-TiO2 films have lower band gap energy than that of undoped-TiO2, extending the absorption of TiO2 into visible region. Diffuse reflectance spectroscopy (DRS) shows that the presence of rutile nanoparticles in photoanodes may improve the photovoltaic performance of solar cells due to better light scattering ability of rutile than anatase phase. The DSC stabilised with 3 at. % Nb (i.e., PN3) had the highest power conversion efficiency of 7.38 % as a result of less recombination, which is demonstrated by electrochemical impedance spectroscopy (EIS). © 2016 Springer Science+Business Media New York Source


Bakhshayesh A.M.,SUN Nanotechnologists Company | Bakhshayesh N.,SUN Nanotechnologists Company
Journal of Sol-Gel Science and Technology | Year: 2015

Abstract: This study comes up with a uniform electrode containing Sr,Nb co-doped TiO2 particles for dye-sensitized solar cell applications. The spherical particles with the average diameter around 2.5 µm are composed of small nanoparticles with the average grain size of 60 nm. X-ray diffraction reveals that the introduction of dopants not only inhibits the growth of rutile phase, but also results in smaller primary crystallites, improving the surface area and dye adsorption ability of the electrodes. X-ray photoelectron spectroscopy shows Sr2+ and Nb5+ ions to be well incorporated into the titania crystal lattice without forming specific strontium or zinc compositions. UV–Visible spectra show that the co-doped TiO2 films have lower band gap energy than the undoped-TiO2, extending the absorption of TiO2 into visible region. Isolated energy levels in the band structure of TiO2 as well as local lattice distortions due to dopants introduction are the parameters that enhance the short-circuit current density of the cells. The TiO2 DSC co-doped with 0.075 at% Sr and 3 at% Nb (i.e., S7N3 cell) has the highest power conversion efficiency of 7.97 % as a result of less recombination, which is demonstrated by electrochemical impedance spectroscopy. Graphical Abstract: [Figure not available: see fulltext.] © 2015 Springer Science+Business Media New York Source

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