| 1. |
- Imani, Roghayeh, et al.
(författare)
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Fabrication of Microfibre-nanowire Junction Arrays of ZnO/SnO2 Composite by the Carbothermal Evaporation Method
- 2014
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Ingår i: Nanomaterials and Nanotechnology. - : SAGE Publications. - 1847-9804. ; 4, s. 21-
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Tidskriftsartikel (refereegranskat)abstract
- A cotton-like ZnO/SnO2 nanocomposite was grown by the carbothermal evaporation of a mixture of ZnO and SnO2 powders at 1100 degrees C by the vapour-liquid-solid process, in which the Sn particles produced by the reduction of SnO2 act as the catalyst. Field-emission scanning electron microscope images suggest that the composites are made of microfibre-nanowire junction arrays. The structure is formed due to the fast growth of the ZnO microfibre and the subsequent epitaxial radial growth of the ZnO nanowires with Sn particles at the tips. The photovoltaic performance of the ZnO/SnO2 nanocomposite sensitized with a D35-cpdt dye was investigated. A dye-sensitized solar cell (DSSC) with a ZnO/SnO2 nanocomposite photoanode based on a cobalt electrolyte achieved a solar-to-electricity conversion efficiency of similar to 0.34% with a short circuit current (JSC) of 0.66 mA/cm(2), an open circuit voltage (VOC) of 870 mV, and a fill factor (FF) of 59. The results show the potential of this one dimensional structure in cobalt electrolyte-based DSSCs; the further optimization which is needed to achieve higher efficiencies is also discussed.
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| 2. |
- Park, Byung-wook, et al.
(författare)
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Understanding Interfacial Charge Transfer between Metallic PEDOT Counter Electrodes and a Cobalt Redox Shuttle in Dye-Sensitized Solar Cells
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:3, s. 2074-2079
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Tidskriftsartikel (refereegranskat)abstract
- Conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with iron(111) tris-p-toluenesulfonate (PEDOT:Tos) having metallic conductivity was coated onto fluorine-doped tin oxide (FTO) glass and plain glass substrates and used as a counter electrode (CE) in a dye-sensitized solar cell (DSC) with a [Co(bpy)(3)](3+/2+) complex redox shuttle. DSCs with PEDOT:Tos/glass CE yielded power conversion efficiencies (PCE) of 6.3%, similar to that of DSCs with platinized FTO glass CE (6.1%). The PEDOT:Tos-based counter electrodes had 5 to 10 times lower charge-transfer resistance than the Pt/FTO CE in DSCs, as analyzed by impedance spectroscopy. More detailed studies in symmetrical CE-CE cells showed that the PEDOT:Tos layers are nanoporous. Not all internal area can be used catalytically under solar cell conditions and effective charge-transfer resistance was similar to that of Pt/FTO.
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| 3. |
- Pazoki, Meysam, et al.
(författare)
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Ab initio study of electronic effects in the ZnO/TiO2 core/shell interface : application in dye sensitized solar cells
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:1, s. 301-307
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Tidskriftsartikel (refereegranskat)abstract
- Core/shell structure of ZnO nanowires coated with a monolayer of TiO2 is investigated using Density Functional Theory (DFT). The electronic states of the semiconductor is calculated and compared before and after coating of the TiO2 monolayer on a ZnO [10 (1) over bar 0] surface. The effect of TiO2 coating induce surface states changes and shifts the conduction and valence band edges to higher energies. Our results, in qualitative agreement with the experimental work of Matt Law et al. (J. Phys. Chem. B, 110, 22652), show an increase in open circuit voltage and a decrease in short circuit current in ZnO/TiO2 core shell dye sensitized solar cells. Regarding the semiconductor density of states (DOS), TiO2 coated ZnO have more conduction band acceptor states and lower electronic back recombination in agreement with experimental results. Surface dipoles are attributed to changes of the local density of states of the surface. This method can be used for more investigation of starting effects of semiconductor interface and helps the study of surface states and their physical origin in dye sensitized solar cells.
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| 4. |
- Pazoki, Meysam, et al.
(författare)
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CVD-grown TiO2 particles as light scattering structures in dye-sensitized solar cells
- 2012
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 2:32, s. 12278-12285
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Tidskriftsartikel (refereegranskat)abstract
- Chemical vapour deposition (CVD) at atmospheric pressure, using TiCl 4 as a precursor, was used to grow nanostructured TiO2 films on glass substrates. At relatively low temperatures (∼245 °C) and using relatively high reactant concentrations, different nano-morphologies of TiO2 were formed simultaneously, such as spheres, nanowires and mesoporous structures. The TiO2 spheres were successfully applied as light-scattering particles in dye-sensitized solar cells, either by direct deposition onto electrodes in the reactor, or by preparation of a printing paste from the deposited particles. For dye-sensitized solar cells using the organic dye D35 as sensitizer and a cobalt-complex based redox electrolyte, a solar cell efficiency of 4.4% was obtained using a 5 μm transparent mesoporous TiO 2 layer. Addition of a 5 μm light-scattering CVD-particle film increased the efficiency by 22% to 5.4%, which was similar to the result obtained with an equally thick commercially available light-scattering film (5.3%). Longer electron lifetime was found using CVD-based films, which is attributed to the presence of more traps in the bulk of the material.
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| 5. |
- Pazoki, Meysam, et al.
(författare)
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Mesoporous TiO2 Microbead Electrodes for Cobalt-Mediator-Based Dye-Sensitized Solar Cells
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:30, s. 16472-16478
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Tidskriftsartikel (refereegranskat)abstract
- Light scattering, porosity, surface area, and morphology of TiO2 working electrode can affect the power conversion efficiency of dye -sensitized solar cells dramatically. Here mesoporous TiO2 microbeads were tested as working electrode in dye-sensitized solar cells based on cobalt tris-bipyridine electrolyte. Power conversion efficiencies up to 6.4% were obtained with D35 dye adsorbed onto the light-scattering microbeads. Electron transport, studied using small light perturbation methods, was found to be significantly faster in the microbead films than in standard mesoporous TiO2 films. This was attributed to the favorable assembly of nanocrystals in the microbeads, which can increase the electron diffusion coefficient in the conduction band. Electron lifetimes were similar in both types of film. While solar cell performance of microbead films was comparable to that of standard mesoporous films in acetonitrile-based electrolytes, a significant improvement was found when the more viscous 3-methoxypropionitrile was used as solvent for electrolyte.
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| 6. |
- Pazoki, Meysam, et al.
(författare)
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Mesoporous TiO2 microbead electrodes for solid state dye-sensitized solar cells
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:91, s. 50295-50300
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous TiO2 microbead films have been investigated as working electrodes for solid state dye sensitized solar cells and 3.5% efficiency was achieved for 4 micrometer thick films under 1 sun illumination. Compared to conventional mesoporous solar cells, microbead films have higher porosity, increased open circuit voltage, lower fill factor and current density, faster transport time and lower electron lifetime. Cross sectional scanning electron microscopy results show that the pore filling of a solid hole conductor (spiro-OMeTAD) inside the entire mesoporous bead film is very good even for 4 micrometer thick films. The high porosity of the microbead film allows good penetration of spiro in thick films, while its high surface area ensures good dye coverage. X-ray photoelectron spectroscopy data reveals a lower density of intra-bandgap trap states for microbead films compared to conventional mesoporous TiO2 films, which could be in part responsible for faster transport of electrons and higher voltage in microbead films. Optimization of microbead films for solid state dye sensitized solar cells can be an interesting possibility for highly efficient and relatively thick film solid state solar cells.
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| 7. |
- Pazoki, Meysam, et al.
(författare)
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The effect of dye coverage on the performance of dye-sensitized solar cells with a cobalt-based electrolyte
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:18, s. 8503-8508
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Tidskriftsartikel (refereegranskat)abstract
- The effect of dye coverage of the mesoporous TiO2 electrode on the performance of dye-sensitized solar cells based on the cobalt tris(bipyridine) electrolyte and the D35 dye was studied in detail. The dye coverage was controlled by using a dye bath with different dye concentrations and containing an inert salt, LiClO4, which was found to promote equilibrium conditions in the dye adsorption process. The amount of adsorbed D35 dye on mesoporous TiO2 was reasonably fit using the Langmuir adsorption isotherm, with a binding constant of 55 000 M-1. Upon increasing the dye coverage on the TiO2 electrode, the electron lifetime in the dye-sensitized solar cell increased remarkably, demonstrating the blocking behavior of the D35 dye at the TiO2-electrolyte interface. Consequently, the solar cell efficiency increased dramatically with the D35 dye coverage.
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