| 1. |
- Cappel, Ute B., et al.
(författare)
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Characterization of the Interface Properties and Processes in Solid State Dye-Sensitized Solar Cells Employing a Perylene Sensitizer
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:10, s. 4345-4358
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Tidskriftsartikel (refereegranskat)abstract
- We recently reported on a perylene sensitizer, ID176, which performs much better in solid state dye-sensitized solar cells than in those using liquid electrolytes with iodide/tri-iodide as the redox couple (J. Phys. Chem. C2009, 113, 14595-14597). Here, we present a characterization of the sensitizer and of the TiO2/dye interface by UV-visible absorption and fluorescence spectroscopy, spectroelectrochemistry, photoelectron spectroscopy, electroabsorption spectroscopy, photoinduced absorption spectroscopy, and femtosecond transient absorption measurements. We report that the absorption spectrum of the sensitizer is red-shifted by addition of lithium ions to the surface due to a downward shift of the excited state level of the sensitizer, which is of the same order of magnitude as the downward shift of the titanium dioxide conduction band edge. Results from photoelectron spectroscopy and electrochemistry suggest that the excited state is largely located below the conduction band edge of TiO2 but that there are states in the band gap of TiO2 which might be available for photoinduced electron injection. The sensitizer was able to efficiently inject into TiO2, when a lithium salt was present on the surface, while injection was much less effective in the absence of lithium ions or in the presence of solvent. In the presence of the hole conductor 2,2-,7,7-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9-spirobifluorene (spiro-MeOTAD) and LiTFSI, charge separation was monitored by the emergence of a Stark shift of the dye in transient absorption spectra, and both injection and regeneration appear to be completed within 1 ps. Regeneration by spiro-MeOTAD is therefore several orders of magnitude faster than regeneration by iodide, and ID176 can even be photoreduced by spiro-MeOTAD.
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| 2. |
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| 3. |
- Cappel, Ute B, et al.
(författare)
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Electronic structure dynamics in a low bandgap polymer studied by time-resolved photoelectron spectroscopy.
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18:31, s. 21921-9
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Tidskriftsartikel (refereegranskat)abstract
- Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials.
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| 4. |
- Cappel, Ute, et al.
(författare)
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Energy Alignment and Surface Dipoles of Rylene Dyes adsorbed to TiO2 nanoparticles
- 2011
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:32, s. 14767-14774
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Tidskriftsartikel (refereegranskat)abstract
- The energy loss in dye-sensitized solar cells calculated from the energy difference between the lowest electronic transition of the dye and the obtained open-circuit voltage is often 1 eV or even more. To minimize this loss, it is important to accurately determine the energy alignment at the TiO2/dye/redox-mediator interface. In this study, we compared the results from electrochemistry and photoelectron spectroscopy for determining the energy alignment of three rylene dyes, two of which absorb relatively far in the red. The trends observed with the methods were different, as in the former, the energy alignment is measured relative to an external reference and includes contributions from solvent reorganization energies, while in the latter, it is measured relative to the energetics of the TiO2 and is lacking such contributions. The influence of the dyes' dipole moments on the energetics of the TiO2 was also measured and explained some of the differences in trends. Finally, we compared the injection efficiencies of the two red-absorbing dyes and found that the differences in injection efficiencies can be better explained using the energy alignment determined from photoelectron spectroscopy. This shows that the method for measuring the energetics of a DSC should be chosen according to what process one intends to study.
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| 5. |
- Eland, John H. D., et al.
(författare)
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Triple ionization of CO(2) by valence and inner shell photoionization
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 135:13, s. 134309-
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Tidskriftsartikel (refereegranskat)abstract
- Spectra of triply ionized CO(2) have been obtained from photoionization of the molecule using soft x-ray synchrotron light and an efficient multi-electron coincidence technique. Although all states of the CO(2)(+++) trication are unstable, the ionization energy for formation of molecular ions at a geometry similar to that of the neutral molecule is determined as 74 +/- 0.5 eV.
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| 6. |
- Eland, John H. D., 1941, et al.
(författare)
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Wide range double photoionization spectra of N2 and CO2
- 2016
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 646, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- Using a magnetic bottle time-of-flight electron spectrometer we have measured double photoionisation spectra of N2 and CO2 covering the range from threshold up to the triple ionisation energies. The experiments demonstrate the use of a new asynchronous chopper in eight-bunch mode of the synchrotron radiation source SOLEIL. For CO22+ some broad bands in the Auger spectra are found to have multiple resolved counterparts in the photoionisation spectrum. All the bands in the Auger spectra have counterparts in the photoionisation spectra, where extra bands attributed to triplet states are present. In the spectrum of N22+ we suggest reassignment of one band.
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| 7. |
- Fredin, Kristofer, et al.
(författare)
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Solid state dye-sensitized solar cells prepared by infiltrating a molten hole conductor into a mesoporous film at a temperature below 150 degrees C
- 2011
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 161:21-22, s. 2280-2283
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Tidskriftsartikel (refereegranskat)abstract
- Infiltration of a molten hole conductor in a mesoporous film at an elevated temperature exhibits good wetting performance and the procedure is therefore suitable as part of the preparation method for solid state dye-sensitized solar cells. Herein, we present a system prepared by infiltrating 4-(diethylamino)benzaldehyde-1,1)-diphenyl-hydrazone in its molten form at a temperature below 150 degrees C. The system displays a maximum photon-to-current conversion efficiency of about 35%, a value corresponding to an increase of about 5 times in comparison with a previously published system prepared by infiltrating a molten hole-conductor at a temperature exceeding 250 degrees C. By means of comparing charge transport and recombination with the results measured for a liquid analogue, we conclude that whereas the transport rates are similar, recombination is significantly more rapid in the solid-state device.
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| 8. |
- Fredin, Kristofer, et al.
(författare)
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Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells
- 2009
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 159:1-2, s. 166-170
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We describe a method to fill thin films of nanoporous TiO2 with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 mu m below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO2/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.
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| 9. |
- Hahlin, Maria, et al.
(författare)
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A Photoelectron Spectroscopy Study of Z-907 Co-adsorbed with DPA on Nanostructured TiO2 Surfaces
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The surface electronic and molecular properties of mixed dye/coadsorbent sensitized TiO2 surfaces was investigated using photoelectron spectroscopy (PES). The sensitization of the TiO2 was performed using the ruthenium based dye cis-disothiocyanato-(2,2-bipyridyl-4,4-dicarboxylic acid)-(2,2-bipyridyl-4,4-dinonyl) ruthenium(II) (Z-907) together with different concentrations of the coadsorbent decylphosphonic acid (DPA). The investigation showed large variations in surface concentration of Z-907 and DPA depending on the dye/coadsorbent ratio in solution, but that the relative amounts at the surface and in solution substantially differ. Generally the DPA coadsorbents exchange with dye Z-907 molecule and trends in the surface concentration show that each dye molecule is replaced by six coadsorbent molecules. The co-adsorption of DPA induced changes in the S2p spectra, indicating changes in the dye surface interaction. Still, investigation of the frontier electronic structure in the dye sensitized TiO2 surfaces show that co-adsorbtion of DPA do not alter the energy level matching between the dye and the TiO2.
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| 10. |
- Hahlin, Maria, et al.
(författare)
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Electronic and molecular structures of organic dye/TiO2 interfaces for solar cell applications : a core level photoelectron spectroscopy study
- 2010
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 12:7, s. 1507-1517
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Tidskriftsartikel (refereegranskat)abstract
- The electronic and molecular properties of three organic dye molecules with the general structure donor-linker-anchor have been investigated using core level photoelectron spectroscopy (PES). The molecules contain a diphenylaniline donor unit, a thiophene linker unit, and cyanoacrylic acid or rhodanine-3-acetic acid anchor units. They have been investigated both in the form of a multilayer and adsorbed onto nanoporous TiO2 and the experimental results were also compared with DFT calculations. The changes at the dye-sensitized TiO2 surface due to the modification of either the donor unit or the anchor unit was investigated and the results showed important differences in coverage as well as in electronic and molecular surface properties. By measuring the core level binding energies, the sub-molecular properties were characterized and the result showed that the adsorption to the TiO2 influences the energy levels of the sub-molecular units differently.
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