The general theme of this thesis is the investigation of light harvesting materials as solar absorbers. The chapters reported within this thesis can be divided into two domains. The first half concerns issues for the electroformation of uniform copper indium diselenide (CISe) thin films and the latter half investigates surface electrochemical processes exhibited by mesoporous, nanocomposite thin films.
Several strategies were investigated concerning the formation of reproducible, large area (ca. 10 cm2), uniform CISe thin films. The examination of a novel substrate for the electrodeposition of CISe is discussed in chapter 2. Here molybdenum coated glass slides undergo a pre-selenisation to form MoSe2/Mo/glass. The MoSe2 is inert and resistant to chemical attack as well as degenerate in nature. Photoactive CISe films were formed on MoSe2/Mo electrodes to demonstrate their potential as substrates for devices.
The use of a rocking disc electrode for the electroformation of large area (ca. 12.1cm2) copper and CISe films is shown in chapters 3 and 4 respectively. The rocking disc electrode induces mass transport by rocking (vibrating) the cell. The induced convection was investigated by monitoring limiting currents of RuII/III(NH3)63+ and potentiostatic deposition of uniform copper films free from pitting and pores was performed. Under rocking disc conditions it is possible to attain a 1:1 ratio in CuIn films using a tartrate based plating bath. Films are selenised to form CISe and as a by-product CuxSe. The photoactivity of the films is non-uniform and patchy due to the presence of CuxSe and/or pin holes which occur from either under or over etching the film. Various post selenisation treatments were performed to improve the photoactivity of the films such as the dilution of etchant, re-annealing the CISe film and the use of an oxidising agent in conjugation with the etchant.
The second part of this thesis investigates the surface electrochemistry of nanocomposite films Fe2O3 and di-ruthenium-bis(benzimidazolyl)pyridine – TiO2 which are shown in chapters 5 and 6, respectively. Mesoporous Fe2O3 thin films exhibit a higher oxidation state which is likely to be a key intermediate for the oxidation of water. By using the spectro-electrochemical methods potentialmodulated spectroscopy and light induced spectroscopy it is possible to attain in situ transmission spectra of this state. The spectra correspond to a surface trapped hole which has been reported by others. The frequency dependence of this surface state was investigated and correlated with theory.
In the final experimental chapter films composed of an inorganic di- ruthenium-bis(benzimidazolyl)pyridine complex (Ru2) and TiO2 nanoparticles were produced. The films exhibited an immobilised Ru signal. Using focus ion beam methods the creation of a nano-trench in a film of ITO was undertaken. The immobilisation of this material within the trench allowed bi-potentiostatic experiments to be conducted which evaluated the charge diffusion processes. An apparent diffusion coefficient of Dapp = 2.5 x 10-15 ms-2 was attained using generator and collector experiments. The potential use of these junction electrodes for other nanocomposite materials is highlighted.
|Date of Award||31 May 2012|
|Supervisor||Frank Marken (Supervisor)|