Self-assembled bilayers consisting of a monolayer of molecules, a metal linking ion and a second molecular layer were prepared and used in controlling critical energy and electron transfer events in dye-sensitized solar cells (DSSCs). DSSCs have shown promise as an alternative to traditional silicon solar cells due to their ease of fabrication and lower manufacturing costs. Despite the high efficiency to cost ratio, DSSCs face the limitations of detrimental recombination across the dye-semiconductor interface as well as narrow absorption transitions which respectively lower the open circuit voltage and short circuit current of these cells. Bilayers consisting of a bridging molecule, zirconium metal ion and N3 dye were assembled on a nanocrystalline metal oxide electrode as a means of inhibiting deleterious recombination processes in DSSCs. Bilayer formation was confirmed by ATR-IR and UV−vis spectroscopy. Interfacial electron transfer events in DSSCs were characterized by electrochemical and photophysical measurements. The results show an increased electron lifetime, diffusion length and open circuit voltage with increasing bridge length. The increased separation between the TiO2 and dye however also reduced injection rate, by extension, photocurrent and the overall efficiency of the DSSC devices. Self-assembled bilayer was also used to achieve broadband light harvesting in DSSCs by incorporating two complementary absorbing dyes. The bilayer here consisted of a monolayer of pN3 dye, zirconium metal ion and p1M dye. The UV-vis and ATR-IR absorption spectra of the bilayer were found to be the sum of the individual dyes. The bilayer devices also demonstrated about 10% higher photocurrent, voltage and power conversion efficiency over the monolayer DSSCs. This was attributed to slower recombination losses at the TiO2-dye1-dye2-electrolyte interfaces as well as higher photon-to-current conversion efficiency across the visible spectrum. A key factor towards the higher performance of the bilayer is directional energy and electron transfer from p1M to pN3 dye. Investigations into the role and properties of the metal ion when coordinated to a dye was further performed to understand how the nature of the metal ion influence the dynamics of the different processes at the dye-semiconductor interface. This can allow optimization of the bilayer architecture and enable its use for an even wider range of applications. 8 different metal ions were studied and coordination to the dye was confirmed by XPS, ATR-IR and UV-vis. Metal ion coordination had minimal influence on energetic levels of the dye with minimal shifts observed. Results suggest that electrostatic interactions between the metal ion and the iodide/triiodide species in the electrolyte as a primary determining factor in the rates of regeneration, back electron transfer and recombination processes as well as the photovoltaic parameters. A remarkable improvement of 130 mV was achieved with two of these metal ions. X-ray photoelectron spectroscopy was used to study the effect of zinc and zirconium metal ion treatment on the core binding energies of un-sensitized and sensitized TiO2 thin films. The metal treatment included treating the TiO2 film with metal ions without further treatment (TiO2 (Mn)) as well as prior to dye sensitization (TiO2 (Mn)-N3). Metal coordinated samples were also prepared (TiO2-N3-Mn). The results indicate there is no change in chemical state of the TiO2 but suggest that zinc treatment might have significant influence on the sulphur atom in the N3 dye. This interaction may also be a clue as to its perturbed diode behavior. / A Dissertation submitted to the Materials Science and Engineering Program in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 13, 2018. / bilayer, dssc, electron transfer, recombination, self-assembled / Includes bibliographical references. / Kenneth Hanson, Professor Directing Dissertation; Simon Foo, University Representative; Hanwei Gao, Committee Member; Eric Hellstrom, Committee Member; Zhibin Yu, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_653483 |
| Contributors | Ogunsolu, Omotola Olukemi (author), Hanson, Kenneth G. (professor directing dissertation), Foo, Simon Y. (university representative), Gao, Hanwei (committee member), Hellstrom, Eric (committee member), Yu, Zhibin (committee member), Florida State University (degree granting institution), Graduate School (degree granting college), Program in Materials Science (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (168 pages), computer, application/pdf |
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