Lead sulfide quantum dot-based nanostructured solar cells

The use of PbS quantum dots (QDs) acting as light absorbers in a range of nanostructured solar cell devices has been investigated. The impact of different QD deposition methods, of the nature and structure of different metal oxides serving as electrodes, as well as interface and surface effects on device performance has been explored. Chapter 3 describes the application of in situ grown PbS QDs as absorber layer for extremely thin absorber solar cells with the inorganic solid hole transporter CuSCN. A polystyrene-block-poly(ethylene oxide) block copolymer was employed as a structure-directing agent for the synthesis of mesoporous TiO2 metal oxide thin films with high surface area and ordered porous structure. Chapter 4 outlines further work in which water-solubilized ex situ grown QDs capped with L-glutathione ligands were employed in order to improve the loading of the PbS QDs onto the internal surface of the porous oxide. Successful sensitization was achieved by inducing opposite surface charges on the surfaces of the QDs and the oxide in order to attract and attach QDs onto the surface of the porous supporting oxide film. The sensitized TiO2 electrodes were used to make efficient liquid electrolyte quantum-dot-sensitized solar cells (QDSCs). Chapter 5 describes the use of SnO2, which has a lower lying conduction band than TiO2, to fabricate scaffolding electrodes that were sensitized with water-solubilized PbS QDs. Passivation of the SnO2 electrodes with a thin layer of MgO, TiO2 and a combination of both was utilized to investigate the effect of surface treatments on the performance of solid-state QDSCs, using Spiro-OMeTAD as organic hole transporter. Chapters 6 and 7 deal with different approaches towards interface tuning in solid-state QDSCs. This part of the work involved the study of solar cell devices utilizing in situ grown PbS QDs with and without organic and inorganic surface passivation, and ex situ grown PbS QDs anchored on mesoporous TiO2 via organic linker molecules. The performance of the fabricated solar cells was evaluated with standard current-voltage and incident-photon-to-collected-electron efficiency measurements, and physical parameters of the devices were characterised with frequency- and time-resolved techniques such as electrochemical impedance spectroscopy, intensity-modulated photovoltage/photocurrent spectroscopy, and open circuit voltage decay measurements, respectively. Overall, the work highlights the importance of surface passivation of QDs, loading of the QDs onto porous semiconducting oxide electrodes, as well as the significance of interfacial effects between QDs, oxides and hole transporter to achieve high-efficiency devices.