Now showing 1 - 3 of 3
  • Publication
    First-principles study of the excited-state properties of coumarin-derived dyes in dye-sensitized solar cells
    Using Time-Dependent Density Functional Theory (TD-DFT), we have investigated the optical properties of dye-sensitized solar cells (DSSCs) comprised of TiO2 nanoparticle sensitized with two coumarins, namely, NKX-2311 and NKX-2593. The two sensitizers (dyes) differ only in their linker moieties and are shown to have different absorption spectra when adsorbed on to the TiO2 surface. Knowledge of different light absorption and charge transfer (CT) behavior within these complexes is useful for further improving the photo-dynamics of newer organic dyes presently being designed and investigated worldwide. Moreover, we have also investigated the effect of deprotonation of the sensitizers' carboxylic groups during adsorption on the titania surface and the excited state electronic properties of the resulting species.
      1277Scopus© Citations 52
  • Publication
    Functional Assessment for Predicting Charge-Transfer Excitations of Dyes in Complexed State: A Study of Triphenylamine-Donor Dyes on Titania for Dye-Sensitized Solar Cells
    (American Chemical Society, 2012-12-13) ; ;
    Time-dependent density functional theory (TD-DFT) was employed to calculate the UV/vis spectra for three of the triphenylamine (TPA)-donor dyes, TC1, L1, and LJ1, in isolation as well as when complexed with a titania nanoparticle. TPA-donor dyes are a class of promising organic dyes for use in dye-sensitized solar cells (DSSCs). The three dyes studied here are among the smallest of these molecules and provide important insight into the entire series of TPA dyes that are being explored as possible sensitizers in titania-based DSSCs. An attempt to calculate the optical spectra for these dyes within the B3LYP approximation to the exchange correlation functional produces erroneous results. However, Coulomb attenuated approximation (CAM-B3LYP) captures the correct photophysics of the dyes and produces more accurate charge-transfer excitation energies of their complexes with titania. This work shows that the extent to which a given approximation fails or succeeds to correctly predict the charge-transfer excitation energies in the isolated dyes is propagated in that it fails (or succeeds) to correctly predict the values of the excitation energies for the complexes. It is, therefore, important to determine the most appropriate functional for a dye before considering it in more complicated structures such as dye-titania complexes.
      567Scopus© Citations 50
  • Publication
    A TD-DFT study of the effects of structural variations on the photochemistry of polyene dyes
    We report a TD-DFT study of three polyene dyes namely: NKX-2553, NKX-2554 and NKX-2569 in isolation as well as upon their adsorption on TiO2 nanoparticles. By choosing closely related dyes we wish to focus on the effects of structural variations on the absorption and charge-transfer properties of these systems. These three dyes show a non-intuitive trend in their respective efficiencies and therefore, were chosen to shed light on the structural components that contribute to this behaviour. Although, NKX-2554 has an additional donor group, it is less efficient compared to the simpler NKX-2553 dye that contains only one donor group. When NKX-2554 structure is slightly modified by lengthening the linker-group, one obtains the most efficient dye among this set, namely, NKX-2569. In this work, we show that the changes in the donor moiety has very little or no effect on the efficiency of these dyes as can be seen in the case of NKX-2553 and NKX-2554. On the other hand, the improved performance of NKX-2569-titania complex can be understood to be a result of the longer linker group. A better understanding of these properties within different dye-titania complexes is important for the continual improvement of DSSCs. In this regards, this study will serve to provide guidelines to improve efficiencies of novel organic dyes.
      790Scopus© Citations 39