One of the main contributions of this thesis is the improvement on the overall performance of the solar cells due to the impact of the surface engineering of silicon nanocrystals (SiNCs) and also down conversion of high energy photons by SiNCs. It is demonstrated that surface engineering techniques by using microplasma processing improve the capabilities of the SiNCs for different opto-electronic applications and in particular for solar cells. Surface engineering of SiNCs in water shows long term stability, which could allow the deployment of SiNCs for a wider range of applications. Microplasma-induce liquid chemistry on SiNCs in ethanol and water shows very unique surface properties which are not achievable by other techniques. The optical and electronic properties of SiNCs/polymer colloid and nanocomposites have been analyzed. It has been found that microplasma processed SiNCs/polymer nanocomposite shows improved optical properties and also exhibits enhanced photogeneration and conductivity. This thesis is focused on the application of SiNCs in photovoltaic devices. Hybrid bulk heterojunction solar cells and SiNCs-Schottkey barrier photo voltaic devices have been developed. Hybrid bulk heterojunction solar cells have polymers and SiNCs as an active layer. A range of different device structures have been produced and investigated with support from current-voltage characteristics, which contributed to identify band alignment and the suitability of the architectures for the solar cells. The results also explain the limitations of the solar cells due to either dissociation and/or transport properties. SiNCs based nanocomposites are being employed as an optical converter first time in organic solar cell. SiNCs/polymer nanocomposite allows down conversion of high energy photons demonstrating a drastic improvement in solar cell efficiency with concentrated light.

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The use of concentrating systems has a great potential to become the lowest-cost PV option if the high energy flux in the concentrated PV module can be utilised efficiently. In this study, a PV module with isolated cells was designed and fabricated with the purpose of examining the performance of each cell under concentrated (using CPC and V-trough) and non-concentrated light. Before the experimental characterisation, a detailed optical analysis for the CPC and V-trough collectors was undertaken. It was found that in spite of both concentrators having the same concentration ratio and aperture area, the angular acceptance and optical efficiency for the CPC were always higher than those of the V-trough for incidence angles above ± 20° and ± 10° , respectively. A comparison of flux distribution on the absorber of the two concentrators indicated that the energy flux was more uniform in the V -trough collector than in the CPC collector. The experimental energy flux concentration for the CPC collector (at normal incidence angle) varied from 0.9 to 3.6, with higher irradiance concentrated near the edges of the PV module. As a result, the CPC performed better with cells located near the edges of the PV module than those at the centre. On the other hand, the energy concentration for the V -trough collector varied from 1.3 to 2.5, with higher irradiance concentrated at the centre of the PV module. The use of the CPC and V-trough concentrators increased the power output of a PV module by 25% and 46%, respectively, compared to a similar non-concentrated PV module. The fabricated isolated cells PV module was used to evaluate, theoretically and experimentally, the energy flux distribution on the surface of a concentrated PV module under CPC and V -trough concentrators. From the analysis, it was found that in both collectors, the experimental optical efficiency (indoor and outdoor) results follow the theoretical ones with reasonable accuracy, especially the outdoor experimental results. The comparison between outdoor and indoor experimental optical efficiencies in each collector showed that there was good agreement between the two results, both for low and high incidence angles. The effects of non-uniform illumination on the performance of a single standard PV cell, at low and medium energy flux concentration ratios as well as the effect of orientation, size and geometrical shapes of non-uniform illumination were studied. It was found that the effect of non-uniform illumination on various cell performance parameters becomes noticeable at medium energy flux concentration ratio. The results also indicated that the performance of a single conventional PV cell depends neither on the location and size of the non-uniform illumination nor the geometrical shape of the non-uniform illumination. A novel hybrid PV cell consisting of low and high efficiency PV cells was designed and fabricated. The electrical energy produced by the hybrid cell was compared, theoretically and experimentally, with a similar low efficiency single PV (LESPV) cell in a low- concentrating symmetric CPC suitable for facade, sloping roof, flat roof and rear side building integration. Both results, simulation and experimental, showed that the daily electrical energy produced by a hybrid cell for different Belfast (UK) sky conditions was higher than that of the LESPV cell, but not to the expected value.

At the Daresbury Laboratory Synchrotron Radiation Source X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) were used to investigate the interfaces of the dye sensitised solid state solar cell. Single crystal (101), nanoparticulate and mesoporous titanium dioxide (TiOz) surfaces were examined using valence band and core level spectra to understand the electronic interactions at heterointerfaces with copper iodide (Cul) and bi-isonicotinic acid (BINA). Photoemission spectra of the anatase (101) single crystal TiO₂ nanoparticulate Ti0₂ surface show their electronic structures are similar but differences exist due to the number of defect states and the differences in band gap due to quantum confinement.