>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nanosized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-tocurrent conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles. Modification of TiO2 with non-metals leads to optical bandgap narrowing, improvement in electron conductivity and increased electron lifetime in the ETL layer. However, a lot of scope exists in understanding and fully quantifying the relationship between optical property, for example light transmission and bandgap modification, versus the doping concentration and type. Most doping approaches are in-situ and involve the addition of a dopant precursor (usually a salt) during the synthesis of TiO2 nanostructures – this invariably leads to uncontrolled doping levels, anion contamination and poor-quality materials – a need thus exists to develop simple, controllable doping approaches. One such approach, which forms the basis of this study, is ex-situ doping by means of plasma generated species in a controlled environment. This field of study is fairly novel and not widely studied, requiring more research to understand the doping mechanisms and influence on the optical and electronic properties of the underlying nanomaterials. In particular, controlled doping of TiO2 with nitrogen using radio-frequency generated (RF) plasma requires vigorous experimentation and characterisation. Inaccuracy of the deposition parameters during exposure remains a common drawback for this approach in addition to a lack of understanding of the surface interaction between the N2 species and specimen during irradiation.

>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nano-sized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-to-current conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles.

>Magister Scientiae - MSc / Perovskite solar cells have attracted a tremendous amount of research interest in the scientific community recently, owing to their remarkable performance reaching up to 22% power conversion efficiency (PCE) in merely 6 to 7 years of development. Numerous advantages such as reduced price of raw materials, ease of fabrication and so on, have contributed to their increased popularity.

Currently organic-inorganic hybrid perovskite solar cells (PSCs) is one kind of promising photovoltaic technology due to low production cost, easy fabrication method and high power conversion efficiency. Charge transport layers are found to be critical for device performance and stability. A traditional electron transport layer (ETL), such as TiO2 (Titanium dioxide), is not very efficient for charge extraction at the interface. Compared with TiO2, SnO2 (Tin (IV) Oxide) possesses several advantages such as higher mobility and better energy level alignment. In addition, PSCs with planar structure can be processed at lower temperature compared to PSCs with other structures. In this thesis, planar-structure perovskite solar cells with SnO2 as the electron transport layer are fabricated. The one-step spin-coating method is employed for the fabrication. Several issues are studied such as annealing the samples in ambient air or glovebox, different concentration of solution used for the samples, the impact of using filter for solutions on samples. Finally, a reproducible fabrication procedure for planer-structure perovskite solar cells with an average power conversion efficiency of 16.8%, and a maximum power conversion efficiency of 18.1% is provided.