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  • 1. Beermann, N.
    et al.
    Boschloo, Gerrit
    Hagfeldt, A.
    Trapping of electrons in nanostructured TiO2 studied by photocurrent transients2002In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 152, no 03-jan, 213-218 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 2. Boonyavong, Narumon
    et al.
    Suwanruji, Potjanart
    Hannongbua, Supa
    Li, Fei
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Karpkird, Thitinun M.
    Synthesis, electrochemistry and photo-induced electron transfer of unsymmetrical dinuclear ruthenium osmium 2,2 '-bipyridine complexes2014In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 287, 40-48 p.Article in journal (Refereed)
    Abstract [en]

    Four unsymmetric dinuclear ruthenium and osmium complexes, Os(bpy)(3)-viologen-Ru(bpy)(3) (1; bpy= 2,2'-bipyridyl), Ru(bpy)(3)-viologen-Ru(bpy)(dcbpy)(2) (2; dcbpy= 4,4'-dicarboxy1-2,2-bipyridyl), Os(bpy)(3)-viologen-Ru(bpy)(dcbpy)(2) (3) and rotaxane 1 subset of CB[7] (CB[7] = cucurbit[7]uril), were successfully synthesized. The NMR, electrochemistry and photochemistry studies of these complexes were performed in non-aqueous solutions. The results show that the CB[7] host mainly locates at the butyl linker part of the osmium side in an acetonitrile solution. This binding lowers the oxidation potential of osmium whereas the oxidation potential of ruthenium does not change. The oxidation potential of ruthenium in complexes 2 and 3 is higher due to the electron withdrawing property of carboxylic anchor groups. Analysis with UV-vis spectra shows the viologen radical formation and reversed process of these complexes in non-aqueous solutions.

  • 3. Boschloo, Gerrit
    et al.
    Lindström, J.
    Magnusson, E.
    Holmberg, A.
    Hagfeldt, A.
    Optimization of dye-sensitized solar cells prepared by compression method2002In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 148, no 03-jan, 11-15 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 4. Chen, Ruikui
    et al.
    Yang, Xichuan
    Tian, Haining
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Tetrahydroquinoline dyes with different spacers for organic dye-sensitized solar cells2007In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 189, no 03-feb, 295-300 p.Article in journal (Refereed)
    Abstract [en]

    Novel organic dyes (C1-1, C1-5 and C2-1) with a tetrahydroquinoline moiety as the electron donor, different thiophene-containing electron spacers and a cyanoacrylic acid moiety as the electron acceptor have been designed and synthesized for the application in dye-sensitized solar cells (DSSCs). An interesting relationship between the dye structures, properties, and the performance of DSSCs based on these tetrahydroquinoline dyes is obtained. Although C2-1 dye, which has a rigid electron spacer, has the narrowest action spectrum among these dyes, it gives the highest solar-to-electricity conversion efficiency (eta) of 4.49% (V-oc = 600 mV, J(sc) = 11.20 mA/cm(2), ff = 0.67) of a DSSC under simulated AM 1.5 irradiation (100 mW/cm(2)). Under the same conditions, the eta value of a DSSC based on N3 dye is 6.16%.

  • 5. Itälä, E.
    et al.
    Granroth, S.
    Ha, D. T.
    Kooser, K.
    Levola, H.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Tanzer, K.
    Kukk, E.
    Fragmentation of imidazole, pyrimidine and purine induced by core ionization: Significance of small-scale chemical environment2018In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 356, 283-289 p.Article in journal (Refereed)
    Abstract [en]

    Fragmentation of imidazole, pyrimidine and purine into pairs of cations induced by carbon 1s core ionization was studied. All three molecules favor two-body fragmentation accompanied with a number of hydrogen ejections. In addition, also the formation of CH1,2N+ strongly characterizes the fragmentation of imidazole, pyrimidine and purine. As purine is a fusion of imidazole and pyrimidine rings, the measurements carried out also provided a possibility to study how the fragmentation changes when an isolated imidazole or pyrimidine molecule becomes a part of a larger structure. Furthermore, the previous studies on two pyrimidine derivatives, thymine and uracil, also provide an opportunity to see how the attachment of simple functional groups affect the fragmentation of pyrimidine. The results suggest that the fragmentation of pyrimidine is rather sensitive to any structural or environmental changes, unlike the fragmentation of imidazole.

  • 6. Karlsson, Martin
    et al.
    Yang, Lei
    Karlsson, Marlin K.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Phenoxazine dyes in solid-state dye-sensitized solar cells2012In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 239, 55-59 p.Article in journal (Refereed)
    Abstract [en]

    Several structural modifications have been made to a sensitizer dye based on the phenoxazine core. which was tested in a solid-state dye-sensitized solar cell configuration based on the hole transporting material 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirofluorene. Light-to-power conversion efficiencies between 2.5% and 4.1% are reported herein. The difference in device performance is significantly related to the variations of dye molecular structure, with dye molecules having surface protecting alkoxy-groups yielding better solar cell devices. The phenoxazine dyes were characterized by their light harvesting capabilities and electronic properties such as electron recombination lifetime and chemical dipole moment.

  • 7. Keis, K.
    et al.
    Bauer, C.
    Boschloo, Gerrit
    Hagfeldt, A.
    Westermark, K.
    Rensmo, H.
    Siegbahn, H.
    Nanostructured ZnO electrodes for dye-sensitized solar cell applications2002In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 148, no 03-jan, 57-64 p.Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized photoelectrochemical solar cells constitute a promising candidate in the search for cost-effective and environment-friendly solar cells. The most extensively studied, and to date the most efficient systems are based on titanium dioxide. In this paper, the possibilities to use nanostructured ZnO electrodes in photoelectrochemical solar cells are investigated. Various experimental techniques (e.g. infrared, photoelectron, femtosecond and nanosecond laser spectroscopies, laser flash induced photocurrent transient measurements, two and three-electrode photoelectrochemical measurements) show that the thermodynamics, kinetics and charge transport properties are comparable for ZnO and TiO2. The preparation techniques of ZnO provide more possibilities of varying the particle size and shape compared to TiO2. However, the dye-sensitization process is more complex in case of ZnO and care needs to be taken to achieve an optimal performance of the solar cell.

  • 8. Kong, Zhixia
    et al.
    Zhou, Huizhi
    Cui, Jingnan
    Ma, Tingli
    Yang, Xichuan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    A new class of organic dyes based on acenaphthopyrazine for dye-sensitized solar cells2010In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 213, no 2-3, 152-157 p.Article in journal (Refereed)
    Abstract [en]

    A new class of organic dyes based on acenaphthopyrazine derivatives, containing pyrazine group as the electron acceptor and o-dicarboxyl acids as the anchoring groups were designed and synthesized for application in dye-sensitized solar cells (DSCs). These dyes have short synthesis routes and are easily adsorbed on the surface of TiO2. Under illumination of simulated AM1.5 solar light (100 mW cm(-2)), a total solar energy conversion efficiency (eta) of 4.04% was obtained for the 3-(diphenylamino)acenaphtho[1,2-b] pyrazine-8,9-dicarboxylic acid (AP-1) in the preliminary tests, in comparison with the conventional N719 dye (eta=7.05%) under the same conditions.

  • 9.
    Liao, Haidong
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Stenman, David
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Study of Indigo carmine as radical probe in photocatalysis2009In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 202, no 2-3, 86-91 p.Article in journal (Refereed)
    Abstract [en]

    The feasibility of using Indigo carmine (IC) as a probe of free radical production in photocatalysis was elucidated by comparative studies of its bleaching by gamma radiolysis and TiO2 photocatalysis. The gamma radiation result from pH 3 to 10 shows that both (OH)-O-center dot and HO2 center dot can bleach IC and that the bleaching yields of (OH)-O-center dot is pH independent at similar to 0.7 molecules per (OH)-O-center dot. The quantum yields (phi) of (OH)-O-center dot from Degussa p25 TiO2 photocatalysis from pH 3 to 10 was determined. It was found that phi was about 4% at pH 10 and dropped to below 1% at pH 3. This agrees well with the result of photocatalysis of Fricke dosimetry at pH 1. The effects of some common inorganic anions that may affect photocatalytic systems in technical applications (Cl-, SO42-, Br-, HPO42-, B4O72-, HCO3-/CO32-) was also investigated, showing that these ions does not inhibit the photocatalytic bleaching efficiency of IC.

  • 10. Nour-Mohammadi, Farahnaz
    et al.
    Nguyen, Hoang Thai
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Lund, Torben
    An investigation of the photosubstitution reaction between N719-dyed nanocrystalline TiO2 particles and 4-tert-butylpyridine2007In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 187, no 03-feb, 348-355 p.Article in journal (Refereed)
    Abstract [en]

    The effect of high concentrations of the solar cell additive 4-tert-butylpyridine (4-TBP) on the stability and lifetime of the sensitizer [Ru(Hdcbpy)(2)(NCS)(2)](2-), 2(n-C4H9)(4)N+, (H(2)dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid), known as N719, has been evaluated based on kinetic data obtained from simple model experiments. In these experiments, colloidal solutions of N719-dyed nanocrystalline TiO2 particles in acetonitrile were irradiated with 532-nm laser light in the presence of 0-1 mol/l of 4-TBP. Five degradation products were identified using LC-ESIMS: the 4-tert-butylpyridine substitution product [Ru(H(2)dcbpy)(Hdcbpy)(NCS)(4-TBP)] (SP) and the products [Ru(H(2)dcbPY)(2)(NCS)(CN)], [Ru(H(2)dcbpy)(Hdcbpy)(NCS)(CH3CN)], [Ru(H(2)dcbpy)(Hdcbpy)(NCS)(H2O)] and [Ru(H(2)dcbpy)(2)(CN)(2)] (3-6). The sum of the quantum yields of the five products, Phi(deg) = (1.3 +/- 0.2) x 10(-4), was found to be independent of 4-TBP concentration. Based on this observation, a degradation mechanism was proposed, in which the reaction proceeds through the rate-determining formation of a common intermediate complex, I = [Ru-II(H(2)dcbpy)(2)(NCS)(NCS.)](+). An average degradation rate of k(deg) = 6 x 10(-3) s(-1) was obtained from the value Of Phi(deg) and the back electrontransfer rate, k(back) of the reaction TiO2 + e(-) vertical bar N719(+) -> TiO2 vertical bar N719, obtained by means of photo-induced absorption (PIA) measurements. The lifetime of the solar cell sensitizer N719 was estimated to be between 34 years, based on k(deg) and an average literature value of the regeneration rate, k(reg) = 2 x 10(6) M-1 s(-1), of the reaction between TiO2 vertical bar N719(+) and iodide. We conclude that the addition of 4-TBP to dye-sensitized solar cells (DSSC) does not decrease the lifetime of the N719 dye during normal solar cell operation at room temperature.

  • 11. Quintana, Maria
    et al.
    Marinado, Tannia M.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Nonomura, Kazuteru
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Organic chromophore-sensitized ZnO solar cells: Electrolyte-dependent dye desorption and band-edge shifts2009In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 202, no 2-3, 159-163 p.Article in journal (Refereed)
    Abstract [en]

    An organic chromophore D5 (3-(5-(4-(diphenylamino)styryl)thiophene-2-yl)-2-cyanoacrylic acid) was tested as a sensitizer in photoelectrochemical mesoporous ZnO solar cells. Using thin (similar to 3 mu m) mesoporous ZnO electrodes, high incident photon-to-current conversion efficiencies of up to 70% were obtained, while power conversion efficiencies up to 2.4% were found in simulated sunlight (100 mWcm(-2)). Long dye adsorption times (16h) could be used without aggregation or precipitation of the dye. The composition of the iodide/triiodide-based electrolyte was found to be crucial in optimization of the ZnO-based dye-sensitized solar cell. A high concentration of Li+ ions was found to be shift the ZnO conduction band edge to more negative potential, whereas opposite behavior is found for mesoporous TiO2 cells. It was also found to be detrimental for solar cell performance and stability. Electrolyte-dependent and photoinduced dye desorption from the ZnO electrode was identified as a major stability problem in D5-sensitized ZnO solar cells.

  • 12.
    Rubio Pons, Oscar
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Serrano-Andrés, Luis
    Burget, Dominique
    Jacques, Patrice
    A butterfly like motion as a clue to the photophysics of thioxanthone2006In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 179, no 3, 298-304 p.Article in journal (Refereed)
    Abstract [en]

    A theoretical, quantum-chemical study of the thioxanthone (TX) molecule has been performed at the MP2 and CASPT2 levels of theory. Geometries, absorption energies, and transition and state properties have been investigated. Two conformers have been found very close in energy with planar (P) and non-planar (NP) structures, the latter characterized by a dihedral angle theta = 173.3 degrees representing the bend of the side benzene rings and an out-of-plane angle theta=4 degrees of the C=O bond. Large changes in the relative positions and properties of the two low-lying electronic absorption bands, pi pi* and n pi*, are computed when changing the conformation. As a consequence of the analysis of the TX absorption spectrum it is suggested that TX should be viewed as dynamically changing its conformation between the planar and the non-planar conformations. We coined such behavior as a "butterfly like motion". This dynamic view of the TX structure enables a plausible explanation of the photophysical properties observed for the system.

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