The aim of the Thesis is to design and evaluate the Cd chalcogenide quantum dots (QDs)-based photoanode for solar energy conversion in three critical devices, including photoelectrochemical cell, solar-wastewater fuel cell and solar cell.

The Thesis begins with the fabrication of Mn-doped CdS QDs supported on TiO2 nanotube arrays (TNT) photoanode by the successive ionic layer adsorption and reaction method (SILAR). The introduction of Mn-dopant enhanced the photoelectron lifetime of the composite photoanode. This made available more photoholes for surface transfer, as reflected by the increase in photocurrent. The addition of organic compounds drastically enhanced the photocurrent, given their faster oxidation rates compared to water. However, depending on the type of organic compounds, whether they are direct hole scavengers (formic acid, diethanolamine, triethanolamine) or hydroxyl radical scavengers (methanol, glucose, urea), tend to impart different extent of photocurrents enhancement. While the measured photocurrent was always higher for Mn-doped CdS/TNT than the undoped composite, direct hole scavengers were up to an order of magnitude more efficient in promoting surface holes transfer than that of hydroxyl radical scavengers, under both UV-containing and visible light irradiations. Interestingly, the prolonged photoelectron lifetime induced by the Mn-dopant was highly beneficial in improving the oxidation of hydroxyl radical scavengers.

The second part of the work fabricated solar-wastewater fuel cell (SWFC) using CdTe-sensitized TNT (CdTe/TNT) photoanode and developed a model to predict the generated photocurrent. A systematic study was carried out to catalog the influence of five different organic classes on the photocurrent responses of the photoanodes, showing dependence on the adsorption of the organic substrates and on the associated photocatalytic degradation mechanisms. Simple and short-chain molecules, such as formic acid and methanol are the most efficient in the corresponding carboxylic acid and alcohol groups as a result of increased molar density of molecules on the photoelectrode surface and fast degradation kinetics. A powerful model, based on Langmuir isotherm, was developed to predict the photocurrent induced by organic mixtures. Three crucial parameters of individual organic, including Langmuir coefficient (α), saturated adsorption (Nsat) and molar photoresponse (ζ) were experimentally identified. These parameters were embedded in the model to extrapolate photocurrent enhancement as a result of competitive adsorption on the photoelectrode. Both bare and CdTe-sensitized TNT photoanodes proved the robustness of model, with the latter showing much higher baseline photocurrent. By further examining componential impedance and the effectiveness of Pt carbon counter electrode, the mechanism behind SWFC was well elucidated.

The last part of the work focused on the development of CdS/CdSe QDs cosensitized solar cell (QDSC) and compare their performance when pairing with different cobalt complexes redox mediators. The cosensitization of CdS and CdSe device shows a higher solar efficiency than single QDs-sensitized one as a result of the improved light harvesting. The performance of cosensitized QDSC is strongly dependent on the order of CdS and CdSe respected to the TiO2, which was attributed to the discrepancy in charge transfer properties. By introducing different organic ligands in cobalt complexes, we can tune the redox potential and diffusion coefficient of redox mediators and thus achieve a certain open circuit voltage (Voc) and short circuit current (Jsc), respectively.