Fabrication of solar cells with higher efficiency, simpler processes and lower cost is largely perceived as the ultimate goal for photovoltaic research. To reach such a goal each step needs to be refined and optimized. In this dissertation, a UV-ozone treatment is proposed as a simple and versatile process that can be applied to multiple fabrication steps for improvement. The UV-ozone cleaning method provides comparable surface cleaning quality to more expensive and hazardous industrial standard RCA clean with less chemical used. A good passivation quality was achieved on both n-type and p-type silicon wafer by a silicon oxide/aluminum oxide passivation stack, formed by UV-ozone treatment and ALD. Creating a thin layer of silicon oxide on the silicon wafer surface before depositing the aluminum contact form a metal-insulator-semiconductor (MIS) contact structure, showing low contact resistance for both n-type and p-type wafers. Device performance simulation was performed by Quokka and Sunsolve using experimental results. The simulation results shown promising power conversion efficiency and indicated contact resistance as the key factor in reaching higher efficiency.

<p>Since the first description of Si nanocrystals, research in this field has gone through raid progress and potential applications of Si nanocrystals have been established. There are several methods applicable to the fabrication of Si nanocrystals with one of the most used being ion implantation followed by thermal annealing. Two types of thermal annealing are available for use: furnace annealing (FA) for several hours, normally in an N₂ atmosphere; and rapid thermal annealing (RTA) for a short time (less than a few minutes), again in an inert atmosphere such as N₂. The formation of the nanocrystals then proceeds with decomposition, segregation, diffusion, nucleation, aggregation, growth and crystallization. This formation requires temperatures in excess of 1000^o C such that noticeable photoluminescence may be observed. This thesis explores the fabrication of Si nanocrystals using the McMaster ion implanter and subsequent RTA. The implantation conditions required to form luminescent nanocrystals are determined. For example, for an implantation energy of 10 KeV a minimum dose of 1.5 10¹⁶ ions cm^-2 is required. The relationship between luminescent intensity and post-implantation annealing is also explored. An optimum annealing temperature of 1100^oC is found. For the first time to the author’s knowledge, a study of the effects of thin film thickness on luminescent intensity is conducted. The major conclusions of this thesis are i) a specific thickness of oxide layer has the maximum PL for a fixed implantation energy and implantation dose, ii) PL intensity is inversely proportional with measuring temperature., iii) the type of oxidation process has a large effect on PL intensity.</p> / Master of Applied Science (MASc)

This thesis focuses on the preparation parameter and characterization of boron and boron nitride thin film. System is built composing of designing the geometry, substrate and target holder, pumping parts and plasma generated parts. Experiments with various conditions have been tried and the optimized condition is found for the film growth rate. Many ways of characterization includes: X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy have been tried to identify the material composition.

Solar energy is one of the fastest growing forms of energy generation due to its low cost, lack of emissions, minimal maintenance, and excellent durability. However, like any other technology, it is also not free from defects and degradation, which limit its performance in the real world. Most of the degradation is related to metal contacts, which also happens to be one of the most expensive items in manufacturing, comprising almost half of the cost of converting a silicon wafer into a photovoltaic (PV) cell. Therefore, studying contact degradation to make them reliable and free of defects is the key to achieving high energy yields. High efficiency PV modules that are both cheap and reliable with an extended lifetime ultimately reduce the levelized cost of energy. This study aims to characterize contact degradation in solar cells to identify the root causes of performance losses and develop alternate solutions to metallization. Electrical and optical characterizations were performed on both accelerated-aged and field-exposed solar cells and modules to look for specific performance losses. Furthermore, materials characterization was performed on selected samples to understand the potential root causes and factors affecting the degradation. Unencapsulated solar cells mainly consisting of newer cell technologies and metallization were exposed to acetic acid to simulate field conditions and understand the effect on contact corrosion. Finally, a low-cost novel contact technology called the "transferred foil contact" was developed that can be used as the back contact of a highly efficient silicon heterojunction solar cell, to minimize recombination, and potentially combine cell metallization and interconnection. An overview of the solar energy history and current state-of-the-art is first discussed, followed by a chapter on solar cell device physics and contact technology. The following chapters discuss the different degradation mechanisms in terms of the process-structure-properties relationships of the PV materials.

Ultrashort-pulsed lasers have been used for high precision processing of a wide range of materials including dielectrics, semiconductors, metals, and polymers/polymer composites, enabling numerous applications ranging from micromachining, photonics to life sciences. However, there are challenges when applying this technology in the industry, which requires scale and throughput different from lab use. The goal of this research is to understand how ultrafast laser pulses interact with thin polymers/polymer composite materials and develop a method that is efficient for ultrafast laser processing of these materials. It is a common practice in industrial applications to run the laser at a high repetition rate and hence high average power. However, the heat accumulation under such processing conditions will deteriorate the processing quality, especially for polymers, which typically have a low melting temperature. An analytical solution for two-dimensional modeling of the temperature distribution has been presented and the solution is used to understand the effect of laser parameters on ultrafast laser processing of polypropylene (PP), which is an important polymer for both scientific and industrial applications. Laser cutting experiments are carried out on PP sheets to correlate with the theoretical calculation. This study shows that in laser cutting, the total energy absorbed in the material and the intensity are two important figures of merit to predict the cutting performance. It is found that heat accumulation can be avoided by a proper choice of the processing conditions and the optical properties (i.e. reflectance, transmittance, and absorptance) are important parameters to control processing with ultrafast lasers. To determine the reflectance, transmittance, and absorptance, time-resolved, single-shot measurements are performed in ultrafast laser interaction with polypropylene for a wide range of laser pulse energies. The absorptance during the ultrafast laser interaction with polymers is divided into the different linear and non-linear effective absorption channels and the absorption mechanism of ultrafast laser interaction with polymers in near-infrared wavelength are explained with a model that takes into account different effective absorption channels and suggests that the non-linear absorption originates from vibrational overtone/combination absorption. The enhancement of the absorptance has been investigated for efficiently processing thin polymers with ultrafast lasers by changing pulse duration. It is suggested from this study that the intense shorter pulse (167 fs) is more efficient for surface processing as most of the energy absorbed at the surface due to the strong nonlinear absorption, while a longer pulse (1000 fs) is more efficient for bulk processing for polymers. The results are useful for designing and controlling ultrafast laser processing of polymers and optimizing laser process parameters for the most efficient processing of polymers.

Scanning probe microscopy techniques were used to investigate the desorption of hydrogen passivated silicon to form SiO2 etch masks The application of the etch masks were planned on being used to manufacture silicon nanowires. Low concentration hydrofluoric acid was used to passivate the surface. The surface was selectively depassivated by SPM techniques. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were used to create the masks. The STM system used was found to desorb hydrogen from the surface faster than the STM could image and was considered incapable in the configuration investigated. This led to the use of atomic force microscopy (AFM). Using a conductive tip in contact mode, lithography on the passivated surface was performed. The topography of the lithography was compared to similar works and found to be similar in size. The width was found to be 80nm and the thickness 1nm. The depassivated layers were confirmed to be oxide through electronic force microscopy (EFM). Finally, voltages were swept with the tip in contact with the surface to find the bandgap of the oxide. It was found that the voltage sweeps were severely modifying the tip along with producing inconsistent desorption thicknesses ranging from 0.2 to 12nm. Despite the results from the voltage sweeps, the lithography procedure performed using the AFM was found to be successful.

<p>Incorporating nanoparticles within a polymer to improve the mobility of the filmis one promising way of creating organic thin film transistors (OTFTs) with large mobilities that could be applicable in real world applications. Carbon nanotubes (CNTs)and graphene nanoplatelets (GNPs) are extensively studied for this application. In order to overcome their tendency to aggregate, a method for creating a stable dispersion within both the solution phase and the film is needed. Here an easy method is established for creating a stable dispersion of CNTs or GNPs within a polymer solution which results in excellent OTFT mobility.A non-percolating network of non-covalently functionalized single walled carbon nanotubes was embedded within poly[5,5’-bis(3-dodecyl-2-thienyl)-2,2’bithiophene](PQT-12) thin films for the purpose of enhancing field effect mobility in thin film transistors. The host polymer was used to stabilize the nanotubes in suspension by π orbital overlap caused by simple application of ultrasonication. The stable nanotube suspension was cast into two different device architectures both with excellent mobilities and on/off ratios. The effect of nanotube content on polymer interaction within suspension, film morphology and electrical properties are discussed. A CNT nanocomposite OTFT with enhanced mobility was also tested for applications in vapour sensing. A method is also presented for the creation of graphene nano-platelets (GNPs) for implementation in nano-composite films. Heat treatment of expandable graphite within a vacuum evaporation chamber yielded chemically pure GNPs of a few nanometer thickness. Exfoliating expandable graphite without heat treatment resulted in even higher concentrations but chemically impure GNPs. The material was non-covalently stabilizedwith PQT-12 in a similar method to CNTs and used to create OTFTs with enhanced mobility. The effect of heat treatment parameters and exfoliation conditions on GNP thickness, size and chemical purity are discussed, as well as effect of GNP content on mobility and on/off ratio.</p> / Master of Applied Science (MASc)

<p>Research in the area of improving the efficiency and manufacturability of alternative energy technologies has been of high interest due to the growing environmental concerns of energy resources. Group III-antimonide-based compound semiconductors have been sought after as excellent candidates for photovoltaic conversion of infrared radiation, outside the spectral range absorbed by the currently available crystalline Si solar cells. The major challenge is the GaSb/Si interface is highly lattice mismatched, and inherently heterovalent. This leads to a high density of structural defects, many of which have not been investigated fully. Both optical and electrical properties of such heteroepitaxy thin films are strongly dependent on the periodicity of the crystal lattice, and the presence of extended defects cause perturbations in the lattice periodicity. Therefore the nature of such extended defects must be understood, in order to better manipulate the growth process to minimize their presence. This thesis demonstrates that through the use of conventional transmission electron microscopy, further insight can be gained into understanding the origin, distribution, propagation, and interaction of various extended defects. From this, a couple of ways to systematically suppress some of the defects have also been implemented, and the mechanism by which they induce such a suppression is also discussed.</p> / Master of Applied Science (MASc)

<p>Organic thin film transistors (OTFTs) have attracted great attention in the last couple of decades due to their potential of cost reductions in manufacturing low-end electronic devices through solution processes. Currently, one of the major challenges facing the field of OTFTs is lack of high performance functional organic materials including both organic semiconductors and gate dielectrics for effective device integrations by solution deposition technologies. This thesis focuses on material designs, interfacial compatibilities, and device integrations for high performance OTFTs.</p> <p>Research progresses in the following areas are presented in this thesis. First, novel liquid-crystalline organic semiconductors, 2,5‟-bis-[2-(4-pentylphenyl)vinyl]-thieno(3,2-</p> <p><em>b</em>) thiophene and 2,5‟-bis-[2-(4-pentylphenyl)vinyl]-(2,2‟)bithiophene for OTFT applications were developed. Mobilities of the OTFTs fabricated from these semiconductors reached 0.15 cm2/V.s with high environmental stability. Such high performance is attributed to their ability to form highly ordered molecular structures. Second, a simple effective approach was developed for tuning solubility of a high mobility polythiophene system through engineering its molecular structure. OTFTs fabricated with the newly developed copolythiophenes from an environmentally benign non-chlorinated solvent showed excellent performance with mobility up to 0.18 cm2/V.s. Third, an effective approach to a solution processed gate dielectric Ph.D. Thesis – P. Liu, McMaster University, Chemical Engineering iv</p> <p>design was developed for all solution-processed flexible OTFTs. This was achieved through a dual-layer dielectric structure design comprised of a bottom layer with a UV-crosslinked poly(4-vinyl phenol-co-methyl methacrylate), (PVP-PMMA), and a top layer with a thermally crosslinked polysiloxane. This solution-processed dual-layer dielectric structure enabled all solution-processed high performance flexible OTFTs. Finally, flexible OTFTs were successfully integrated on plastic substrates (PET) from non-chlorinated solvents by using the copolythiophenes and the dual-layer dielectric. The integrated flexible devices showed good OTFT characteristics with mobility up to about 0.1 cm²/V.s.,</p> <p>well defined linear and saturated regions, and a close to zero turn-on voltage.</p> / Doctor of Philosophy (PhD)

<p>The growth of CdTe thin films on Al₂O₃(0001) substrates by pulsed laser deposition from undoped pressed powder targets was studied. Thin film crystal structure was investigated by x-ray texture analysis as a function of plume flux, growth temperature and film thickness. Crystal texture increased for a decrease in plume flux. Single crystal CdTe (111) films were obtained by optimizing the plume flux. Increasing the growth temperature demonstrated a reduction in twin density. An optimum temperature of 300°C minimized the twin density without adverse desorption effects. The twin density decreased as an inverse squared function of film thickness. Single crystal CdTe films with comparable structural quality to Bridgeman single crystal wafers were grown under optimal conditions.</p> <p>The optoelectronic properties of CdTe films were investigated by photoluminescence and photoreflectance spectroscopy. The room temperature bandgap energy of 1.51 eV was consistent between spectroscopic measurements. Broadening parameters for spectra were consistent with reference high quality material. Low temperature photoluminescence spectra had a dominant emission consistent with bound excitons found in bulk CdTe. Emissions consistent with self-compensation or doping were not found. Hall effect and conductivity measurements at 300 K demonstrated high resistivity for undoped material and electron mobilities comparable to bulk CdTe for lightly doped films. Spectroscopic and electrical measurements of high structural quality CdTe films were consistent with high optoelectronic quality.</p> <p>An as-grown ability of the films to detach from their substrate was discovered. X-ray texture analysis and photoluminescence spectroscopy of films released onto rigid secondary carriers demonstrated that they maintained their structural and optoelectronic quality proceeding lift-off. Substrates having films released from them were found to be suitable for repeated growth. The technological relevance of this discovery is likely to drive further study into the lift-off phenomena and controlled doping of CdTe thin films.</p> / Master of Applied Science (MASc)