Computational chemistry and spectroscopic studies of dye-sensitized solar cell materials

Abstract

The work presented in this thesis investigates a series of materials that have utility in dye-sensitized solar cells using density functional theory (DFT) in concert with spectroscopy, including resonance Raman spectroscopy. Chapter 1 provides a survey of how dye-sensitised solar cells fit into the renewable energy landscape. The operation of the cells is also discussed and related to electron transfer theory. The theory of resonance Raman spectroscopy is presented and then aspects of computational chemistry are introduced. Experimental procedures including computational method details are given in Chapter 2. Chapter 3 describes a computational study of a series of salicylic acid based derivatives in which the charge-transfer between the dye and TiO2 is modelled with a (TiO2)6 cluster. The electronic absorption data and electronic structure are correlated with experimental solar cell performance data. Chapter 4 investigates extended salicylic acid dye systems in which a donor group is incorporated. The effect of these groups on electron transfer kinetics is modelled using a number of methods and an evaluation of electron transfer kinetics from dye to TiO2 presented. Chapter 5 uses the electron transfer models introduced in Chapter 4 and extends them to examine injection rates in porphyrin systems. In these systems it is possible to compare calculated with experimental data and it is found that a model in which Marcus-Hush theory includes a continuum of states in the TiO2 conduction band and the occupancy of these states is the most predictive model. Chapter 6 describes the effect of interactions with silane coupling agents and TiO2, a modelled by (TiO2)6. These agents are used as a blocking layer in dye-sensitised solar cells and it is found that their experimental performance may be related to length and molecular volume. Chapter 7 describes the tuning of spectral transitions in porphyrinbased systems via axial ligation with boron moieties and through reduction of the macrocycle to chlorin coupled with extensions of _-conjugation with peripheral substituents. These effect are rather different; in the case of axial ligation of porphyrins although the MOs are similar the spectra change as the molecule becomes saddled. In the case of the chlorin the substituents increase conjugation length.