| 1. |
- Boschloo, Gerrit, et al.
(author)
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Optimization of dye-sensitized solar cells prepared by compression method
- 2002
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In: Journal of Photochemistry and Photobiology A. - 1010-6030 .- 1873-2666. ; 148:03-jan, s. 11-15
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Journal article (peer-reviewed)abstract
- Nanostructured TiO2 films have been deposited onto conducting glass and on flexible conducting plastic substrates using a compression technique. Dye-sensitized solar cells prepared from Degussa P25 TiO2 powder, red dye (Ru(dcbpy)(2)(SCN)(2)) or black dye (Ru(tcterpy)(SCN)(3)) and an electrolyte containing LiI and I-2 in 3-methoxypropionitrile were tested using standard photoelectrochemical techniques. The average overall efficiency of small open cells sensitized with the red dye on plastic substrates was 4.5% (100W m(-2)). In a direct comparison, red and black dye gave about the same efficiencies. For both dyes, addition of 4-tert-butylpyridine to the electrolyte resulted in a decreased IPCE response in the whole spectral range, with a specific decrease in the red region, which is attributed to a shift in the conduction band edge of the nano structured TiO2.
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| 2. |
- Hagfeldt, A., et al.
(author)
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A system approach to molecular solar cells
- 2004
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In: Coordination chemistry reviews. - : Elsevier BV. - 0010-8545 .- 1873-3840. ; 248:13-14, s. 1501-1509
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Research review (peer-reviewed)abstract
- This paper gives an overview of the research and development of dye-sensitized solar cells (DSC) within the Swedish research program 'Angstrom Solar Center'. A path towards low production cost is the development of a continuous process, which allows the production of solar cells in large volumes and with a high productivity. We have developed a deposition method for the production of the mesoporous TiO2, electrode layer that is based on compression of a powder film at room temperature. This technique allows us to use flexible substrates-a prerequisite fora continuous process. A novel interconnect technology, compatible with a continuous production process, is described. Stability data of plastic DSC, exposed to indoor light for more than 10,000 h, demonstrates the possibility for the technology to be explored for various types of indoor applications. Optimization of the DSC is a challenging task as it is a complex highly interacting molecular system. A system approach is proposed, where the complete DSC is investigated with a series of measurement techniques ('toolbox') that allows the study of the internal processes under relevant conditions. Two examples of such techniques are given.
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| 3. |
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| 4. |
- Yanagisawa, M., et al.
(author)
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Synthesis of phthalocyanines with two carboxylic acid groups and their utilization in solar cells based on nanostructured TiO2
- 2004
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In: Journal of Porphyrins and Phthalocyanines. - 1088-4246 .- 1099-1409. ; 8:10, s. 1228-1235
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Journal article (peer-reviewed)abstract
- A way of anchoring unsymmetrical phthalocyaninato-metal complexes (metal ion: zinc and ruthenium) is described. The synthesis and characterization of these complexes are presented. In case of the zinc complex, the obtained product is an aggregate, while only the monomer is obtained in the case of the ruthenium derivative. Both complexes could be attached onto the TiO2 surface by using the reported method. Both dyes are expected to form monolayers with dye molecules standing on the surface of nano-structured TiO2, forming higher-order aggregates with the zinc but not with the ruthenium complex. A highest monochromatic incident photo-to-current conversion efficiency (IPCE) of 1.6% at 690 nm was obtained for a solar cell based on the Pc-Zn sensitized nano-structured TiO2 electrode, while an IPCE of 23% at 630 nm was obtained for the Pc-Ru sensitized electrode. Overall conversion efficiencies (eta) at a simulated AM 1.5 (100 W.m(-2)) of 0.03% and 0.40% for the zinc and ruthenium complexes were achieved, respectively. The difference in efficiencies could be due to the formation of face-to-face aggregation in the former case. This work shows that the ruthenium complex, with two axial methylpyridine ligands, does not form aggregates in solution nor on the surface of TiO2, making it possible for further construction of supramolecular systems with such types of phthalocyanine.
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| 5. |
- Bauer, C., et al.
(author)
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Electron injection and recombination in Ru(dcbpy)(2)(NCS)(2) sensitized nanostructured ZnO
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:24, s. 5585-5588
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Journal article (peer-reviewed)abstract
- The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bypiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films have been investigated by femtosecond and nanosecond spectroscopy. The incident photon to current conversion efficiency (IPCE) for these dye-sensitized electrodes was 36% in the maximum of 530 nm, corresponding to a quantum efficiency of 80%. The highest: IPCE values were obtained when the electrodes were prepared under conditions where formation of dye aggregates in the pores of the nanostructured films is avoided. For such films, the electron injection time was in the subpicosecond regime (< 300 fs), which is comparable to the N719-TiO2 system. The back electron-transfer kinetics between conduction band electrons and oxidized dye molecules were biexponential with time constants of 300 mus and 2.6 us. Variation of the light intensity did not affect the time constants, but only their relative weights. The kinetics of back electron transfer in the N719-ZnO and N719-TiO2 systems were found to be identical.
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| 6. |
- Bauer, C., et al.
(author)
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Ultrafast relaxation dynamics of charge carriers relaxation in ZnO nanocrystalline thin films
- 2004
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 387:03-jan, s. 176-181
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Journal article (peer-reviewed)abstract
- Ultrafast spectroscopy has been used to study the relaxation processes of charge carriers in ZnO nanocrystalline thin films. A broad red-IR absorption band linked to shallowly trapped electrons was observed by spectroelectrochemical measurements. Femtosecond transient absorption data revealed multiexponential decays of the charge carriers with time constants ranging from 1 to 400 ps. The decay profile of the signal shows a probe wavelength dependence. This effect is assigned to the trapping (localisation) of nonequilibrium charge carriers which occurs on a time scale of similar to1 ps. The recombination of shallowly trapped electrons with deeply trapped holes, determined by single-photon counting, mainly occurs in 400 ps.
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| 7. |
- Bauer, C., et al.
(author)
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Ultrafast studies of electron injection in Ru dye sensitized SnO2 nanocrystalline thin film
- 2002
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In: International Journal of Photoenergy (Online). - 1110-662X .- 1687-529X. ; 4:1, s. 17-20
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Journal article (peer-reviewed)abstract
- By using two-color femtosecond transient absorption spectroscopy, we have measured the electron injection rate for bis(tetrabutylammonium) cis di(thiocyanato) bis (2,2-bypiridine-4,4 carboxylic acid) Ruthenium (II) dye ( called N719) into SnO2 nanocrystalline thin films. The electron injection rate has been measured by monitoring the formation of the dye oxidized state and the arrival of electrons in the conduction band. Dynamics of electron injection are multiexponential (0.2, 4 and 130 ps) and are therefore slower than the N719-ZnO or N719-TiO2 systems. The photocurrent action spectrum of N719-SnO2 shows a quantum efficiency of 0.65 at 530 nm proving that efficient charge separation can take place despite of the relatively slow electron injection rate.
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| 8. |
- Beermann, N., et al.
(author)
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Trapping of electrons in nanostructured TiO2 studied by photocurrent transients
- 2002
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In: Journal of Photochemistry and Photobiology A. - 1010-6030 .- 1873-2666. ; 152:03-jan, s. 213-218
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Journal article (peer-reviewed)abstract
- The electron transport in nanostructured TiO2 has been investigated in an electrochemical system using laser flash induced photocurrent transient measurements with additional continuous monochromatic bias light. Significant effects are found on the photocurrent transient depending on the wavelength of the bias light (360-480 nm). The electron transport time is shorter and the total collected charge is higher when the bias light is in the UV region, while increased transport times and a decreased charge is found with visible light bias. These effects can be explained by trap filling by the UV bias light in the first case and by emptying of traps by visible bias light in the latter.
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| 9. |
- Boschloo, Gerrit, et al.
(author)
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Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO2
- 2003
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 370:04-mar, s. 381-386
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Journal article (peer-reviewed)abstract
- Photoinduced absorption (PIA) spectroscopy was used to investigate dye-sensitized electrodes and solar cells under illumination conditions comparable to sunlight. In the absence of redox electrolyte, cis-Ru (dcbpy)(2)(NCS)(2)-sensitized nanostructured TiO2 films show a long-lived photoinduced charge-separation (oxidized dye molecules/injected electrons in TiO2), with a lifetime of about 10(-3) s under full sun illumination. The PIA spectrum of a complete dye-sensitized cell is due to electrons in TiO2 and iodine radicals (12) in the electrolyte. The lifetime of this charge-separated state at open-circuit conditions was determined to be 0.15 s (0.27 sun illumination).
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| 10. |
- Boschloo, Gerrit, et al.
(author)
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Spectroelectrochemistry of nanostructured NiO
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:15, s. 3039-3044
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Journal article (peer-reviewed)abstract
- Transparent nanostructured NiO electrodes have been prepared by heating Ni(OH)(2) sol-gel films at a temperature of 300-320 degreesC. Nanostructured NiO (bunsenite) behaves as a p-type semiconductor and has an indirect band gap of 3.55 eV. It shows a strong anodic electrochromic effect, as it changes color from transparent to brown-black upon application of positive potentials. This effect is caused by oxidation of Ni atoms located at the NiO/electrolyte interface. Electrochemical oxidation reactions are highly reversible in both aqueous and nonaqueous electrolytes. In aqueous electrolyte, the half-potentials show a Nernstian pH dependence, whereas in nonaqueous electrolytes, the type of cation present determines the shape and position of the cyclic voltammogram.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Edwards, M. O. M., et al.
(author)
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'Electric-paint displays' with carbon counter electrodes
- 2001
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In: Electrochimica Acta. - 0013-4686 .- 1873-3859. ; 46:13-14, s. 2187-2193
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Journal article (peer-reviewed)abstract
- 'Electric-paint displays' are electrochromic displays with dyed nanostructured metal-oxide electrodes, e.g. viologen-derivatized nanostructured titanium dioxide electrodes. Such displays are particularly promising for applications with low switch frequency, large segment areas, and high demands on colours, background brightness, and large viewing-angles. The concept is simple and well suited for inexpensive industrial production methods. We present blue-on-white electric-paint displays with porous carbon counter electrodes. The initial results with laboratory prototypes are promising. The switch time is about 1/2 s and the reflectance in the bleached state is as high as 40-55% in the visible region. Furthermore, the display prototypes sustain more than 100 000 switching cycles without severe degradation. The results from spectroelectrochemical measurements on the assembled displays are presented.
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| 15. |
- Gómez, M.M., et al.
(author)
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Dye-sensitized sputtered titanium oxide films for photovoltaic applications : influence of the O2/Ar gas flow ratio during the deposition
- 2003
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In: Solar Energy Materials and Solar Cells. - 0927-0248 .- 1879-3398. ; 76:1, s. 37-56
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Journal article (peer-reviewed)abstract
- Titanium oxide films were prepared by reactive DC magnetron sputtering onto SnO2:F coated glass substrates. The O-2/Ar gas flow ratio was kept at a constant value Gamma during the deposition, and a series of films were deposited with 0.050 < Gamma < 0.072. Structural studies were performed by X-ray diffraction and transmission electron microscopy; the structure displayed penniform features with a clear dependence on F. Charge transport in the films was evaluated by use of time-resolved photocurrents; a diffusion model was fitted to the experimental data and two different transport mechanisms were proposed depending on the film stoichiometry. Dye sensitization in cis-dithiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium (II) was performed to evaluate incident photon-to-current conversion efficiency and solar cell properties of the films. These parameters showed a clear dependence on Gamma. Optical measurements gave evidence for the presence of polaron absorption for the film deposited at Gamma = 0.050.
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| 16. |
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| 17. |
- He, J. J., et al.
(author)
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Phthalocyanine-sensitized nanostructured TiO2 electrodes prepared by a novel anchoring method
- 2001
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:9, s. 2743-2747
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Journal article (peer-reviewed)abstract
- A novel method for anchoring phthalocyanines substituted with ester groups onto nanostructured TiO2 films is described. Such phthalocyanines did not adsorb on nanostructured TiO2 film by the ordinary methods. In our new method, the TiO2 film is pretreated with (CH3)(3)COLi to change the surface hydroxyl groups (-OH) into oxygen anions (-O-), thus making the surface more reactive toward the ester functionalities of the dye. The dye can then be anchored onto the semiconductor surface through the produced carboxylate group(s). The amount of anchored dye on the semiconductor shows a dependence on both the time of base treatment and the time of dye treatment. Electrodes treated with the free base phthalocyanine and zinc phthalocyanine were characterized by absorption spectroscopy, photocurrent action spectroscopy, and photocurrent-photovoltage measurements. The homogeneous blue-green color and the absorption bands in the far-red region are indicative of an attachment of the dye on TiO2 film. A monochromatic incident photo-to-current conversion efficiency of 4.3 % was achieved at 690 nm for a cell where the base-treated electrode was treated with ZnPcBu.
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| 18. |
- He, Jianjun, et al.
(author)
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Modified phthalocyanines for efficient near-IR sensitization of nanostructured TiO2 electrode
- 2002
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:17, s. 4922-4932
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Journal article (peer-reviewed)abstract
- A zinc phthalocyanine with tyrosine substituents (ZnPcTyr), modified for efficient far-red/near-IR performance in dye-sensitized nanostructured TiO2 solar cells, and its reference, glycine-substituted zinc phthalocyanine, (ZnPcGly), were synthesized and characterized. The compounds were studied spectroscopically, electrochemically, and photoelectrochemically. Incorporating tyrosine groups into phthalocyanine makes the dye ethanol-soluble and reduces surface aggregation as a result of steric effects. The performance of a solar cell based on ZnPcTyr is much better than that based on ZnPcGly. Addition of 3alpha,7alpha-dihydroxy-5beta-cholic acid (cheno) and 4-tert-butylpyridine (TBP) to the dye solution when preparing a dye-sensitized TiO2 electrode diminishes significantly the surface aggregation and, therefore, improves the performance of solar cells based on these phthalocyanines. The highest monochromatic incident photo-to-current conversion efficiency (IPCE) of similar to24% at 690 nm and an overall conversion efficiency (eta) of 0.54% were achieved for a cell based on a ZnPcTyr-sensitized TiO2 electrode. Addition of TBP in the electrolyte decreases the IPCE and eta considerably, although it increases the open-circuit photovoltage. Time-resolved transient absorption measurements of interfacial electron-transfer kinetics in a ZnPoTyr-sensitized nanostructured 702 thin film show that electron injection from the excited state of the dye into the conduction band of TiO2 is completed in similar to500 fs and that more than half of the injected electrons recombines with the oxidized dye molecules in similar to300 ps. In addition to surface aggregation, the very fast electron recombination is most likely responsible for the low performance of the solar cell based on ZnPcTyr.
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| 19. |
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| 20. |
- Hjelm, Johan, 1974-
(author)
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Conducting Polymers Containing In-Chain Metal Centres : Electropolymerisation and Charge Transport
- 2003
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Doctoral thesis (other academic/artistic)abstract
- Conjugated polymers that exhibit high electronic conductivities play key roles in the emerging field of molecular electronics. In particular, linking metal centres with useful electrochemical, photophysical, or catalytic properties to the backbone, or within the polymer chain itself, is a topic which has attracted a significant amount of interest lately. Structurally rigid monomers that can be electropolymerised to form highly conducting molecular wires may provide new insights into conduction mechanisms, e.g., exploiting resonant superexchange (electron-hopping) by tuning the energies of redox centre and bridge states. The focus of this thesis lies on the electrochemical investigation of preparation, growth dynamics, and charge transport dynamics of oligothiophene/transition metal hybrid materials. The incorporation of ruthenium(II) and osmium(II) terpyridine complexes into such polymeric assemblies was accomplished by an electropolymerisation procedure, to produce rod-like oligothienyl-bridged metallopolymers. The properties of the monomers used were characterised by optical spectroscopy and electrochemical techniques. Charge transport was studied in detail for some of the materials created, and it was found that the electron transport rate and dc conductivity was enhanced by up to two orders of magnitude compared to relevant non-conjugated polymers, demonstrating the usefulness of this approach for optimization of charge transport in metallopolymers. The charge transport diffusion coefficent was determined to (2.6 ± 0.5) x 10-6 cm2 s-1 for a quaterthienyl-bridged {Os(tpy)2} polymer by use of an electrochemical steady-state method carried out using a transistor-like experimental geometry. It was found that charge transport in these materials is concentration-gradient driven. The rate limiting step of the charge transport process was investigated using electrochemical impedance spectroscopy. The electropolymerisation dynamics of one of the monomers was studied using microelectrodes, and the results obtained shows that electropolymerisation is highly efficient, and indicate that mass transport controls this process. Through a combination of controlled potential deposition and SEM imaging it was demonstrated that it is possible to exploit the edge effect of microelectrodes to promote film growth in a direction co-planar with the electrode surface.
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| 21. |
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| 22. |
- Paulsson, Heléne, et al.
(author)
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Molten and Solid Metal-Iodide-Doped Trialkylsulphonium Iodides and Polyiodides as Electrolytes in Dye-Sensitized Nanocrystalline Solar Cells
- 2004
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In: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 82:3, s. 345-360
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Journal article (peer-reviewed)abstract
- The conductivity and solar cell performance of metal-iodide-doped trialkylsulphonium iodides and polyiodides have been investigated as electrolytes in dye-sensitized nanocrystalline solar cells (DNSCs). Nine different metal-iodide-containing (R2R′S)I with additional iodine provided overall solar-to-electric energy conversion efficiencies of over 2%, while used as electrolytes in DNSCs in simulated AM 1.5 solar light at the light intensity of 100Wm-2. The highest overall conversion efficiency, 3.1%, was achieved by using the electrolyte (Bu2MeS)I: AgI:I2 in the proportions (1:0.03:0.05). The effects from 4-tert-butylpyridine treatment of the electrodes were studied. The effects of metal-iodide doping were also investigated with respect to speciation in the electrolytes and potential influence on electrochemical conductivity.
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| 23. |
- Paulsson, Heléne, et al.
(author)
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Molten and solid trialkylsulfonium iodides and their polyiodides as electrolytes in dye-sensitized nanocrystalline solar cells
- 2003
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 107:49, s. 13665-13670
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Journal article (peer-reviewed)abstract
- Potential new electrolytes for dye-sensitized nanocrystalline solar cells (DNSCs) of Gratzel type based on trialkylsulfonium iodides have been investigated. Room temperature molten salts of (Et2MeS)I, (Bu2MeS)I, and (Bu2EtS)I, with iodine in low concentrations, revealed good conducting abilities. DNSCs using iodine-doped (Bu2MeS)l as electrolyte achieved an overall light-to-electricity conversion efficiency of 3.7% in simulated AM 1.5 solar light at a light intensity of 0.1 Sun. The effects from varying the temperature during the IN measurements were studied, as well as the effects of 4-tert-butylpyridine treatment of the electrodes.
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| 24. |
- Wang, H. L., et al.
(author)
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Electrochemical investigation of traps in a nanostructured TiO2 film
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:13, s. 2529-2533
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Journal article (peer-reviewed)abstract
- Electron traps at the nanostructured TiO2 (anatase)/aqueous electrolyte interface have been studied by means of electrochemical methods. The transient current decays at different potentials positive of the flat band potential clearly illustrate the trap-filling process. The more negative the potential, the shorter the trap-filling period. It is found that most traps locate positive of -0.9 V vs Ag/AgCl at pH 13, or positive of -0.3 V vs Ag/AgCl at pH 4.7. It is proposed that the trap distribution as a function of potential is directly proportional to dQ/dU, i.e., to the current density in a linear sweep voltammetry experiment. The trap densities in aqueous electrolytes are estimated to be 4 x 10(11) cm(-2) (microscopic area) at pH 4.7 and 5 x 10(13) cm(-2) (microscopic area) at pH 13. The pH dependency of the trap density indicates that traps investigated are surface-related.
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