A computational investigation of some optoelectronic applications of carbon nanotubes (CNT) is presented, including CNT-based solar cells and biosensors. The results could be used to evaluate the performance of CNT devices and clarify the necessity of further experimental research in this area. A coaxially-gated CNT field-effect transistor (CNFET) forms the basic structure of the devices modeled in this thesis. Diffusive transport is present in long-channel devices, as in our case, while the quantum mechanical effects are mainly present in the form of tunneling from Schottky-barrier contacts at the metal-CNT interfaces. Band-to-band recombination of electron-hole pairs (EHP) is assumed to be the source of electroluminescence. In a first-order approximation, protein-CNT interactions are modeled as the modification of the potential profile along the longitudinal axis of CNTs due to electrostatic coupling between partial charges, in the oxide layer of the CNFET, and the nanotube. The possibility of electronic detection is evaluated. The electroluminescence of the CNT is proposed as an optical detection scheme due to its sensitivity to the magnitude and the polarity of the charge in the oxide. The validity of the model is argued for the given models. A value for the minimum required size of a computational window in a detailed simulation is derived. The structure of an electrostatically gated p-i-n diode is simulated and investigated for photovoltaic purposes. The absorbed power from the incident light and the interaction between the nanotubes is modeled with COMSOL. The results are interpreted as a generation term and introduced to the Drift-Diffusion Equation (DDE). We have observed behavior similar to that in an experimentally-realized device. The performance of CNT-based solar cells under standard AM 1.5 sunlight conditions is evaluated in the form of an individual solar cell and also in an array of such devices.

While photovoltaic (PV) manufacturing is on track to provide a substantial portion of world electricity generation, the growth of the industry is likely to be lower than desired to meet targets designed to mitigate climate change. Many different PV technologies have been developed, but PV modules based on Si are the dominant technology due to its low cost and relatively high energy conversion efficiencies. PV modules based on III-V materials are primarily used for aerospace applications due to their high cost and record-setting efficiencies. Traditional manufacturing techniques for III-V PV require expensive precursors, and have high capital costs and low throughput. Close-spaced vapor transport (CSVT) is an alternative technique for deposition of III-V materials that was invented in the 1960s but has not been fully developed for the production of PV devices. This work describes progress towards high efficiency solid-state GaAs solar cells produced by CSVT. Previous results have demonstrated good electronic quality of CSVT GaAs using photoelectrochemical cells, but such devices have not been demonstrated to be commercially practical. This work investigates the potential of CSVT to produce high-efficiency III-V PV by fabricating and characterizing GaAs films and simple homojunction solar cells. Chapter I describes the motivation and state of III-V PV research, and establishes basic device physics background. Chapter II gives details of film growth and device design and fabrication. Chapter III gives an overview of the film and device characterization methods employed. Chapter IV explores the primary limitations in the efficiency of the homojunction solar cells fabricated for this study and discusses some practical concerns in translating the technique to a manufacturing environment. Chapter V explores the electronically-active defects in both $n$-type films and in $p$-type absorbers of solar cells, which would be likely to limit the efficiency of devices optimized considering the results presented in Chapter IV. Chapter VI discusses some of the possible future directions for applying CSVT to more advanced device structures which are more commercially relevant, including the growth on alternative substrates and growth of ternary materials for passivating layers or multijunction cells. This dissertation includes previously published and unpublished co-authored material.

A computational investigation of some optoelectronic applications of carbon nanotubes (CNT) is presented, including CNT-based solar cells and biosensors. The results could be used to evaluate the performance of CNT devices and clarify the necessity of further experimental research in this area. A coaxially-gated CNT field-effect transistor (CNFET) forms the basic structure of the devices modeled in this thesis. Diffusive transport is present in long-channel devices, as in our case, while the quantum mechanical effects are mainly present in the form of tunneling from Schottky-barrier contacts at the metal-CNT interfaces. Band-to-band recombination of electron-hole pairs (EHP) is assumed to be the source of electroluminescence. In a first-order approximation, protein-CNT interactions are modeled as the modification of the potential profile along the longitudinal axis of CNTs due to electrostatic coupling between partial charges, in the oxide layer of the CNFET, and the nanotube. The possibility of electronic detection is evaluated. The electroluminescence of the CNT is proposed as an optical detection scheme due to its sensitivity to the magnitude and the polarity of the charge in the oxide. The validity of the model is argued for the given models. A value for the minimum required size of a computational window in a detailed simulation is derived. The structure of an electrostatically gated p-i-n diode is simulated and investigated for photovoltaic purposes. The absorbed power from the incident light and the interaction between the nanotubes is modeled with COMSOL. The results are interpreted as a generation term and introduced to the Drift-Diffusion Equation (DDE). We have observed behavior similar to that in an experimentally-realized device. The performance of CNT-based solar cells under standard AM 1.5 sunlight conditions is evaluated in the form of an individual solar cell and also in an array of such devices. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

With the need for the development of renewable sources of energy, organic photovoltaic (OPV) has been attracting researchers’ interest for the past decades. This solar technology utilizes carbon-based semiconductors instead of conventional inorganic materials which enables inexpensive, lightweight and flexible roll-to-roll fabrication of large area solar panels with a very short energy payback time. Device efficiencies have rapidly increased to above 18% within the last few years, becoming competitive with solar technologies available on the market. However, research has been focused on the maximization of efficiencies at all cost leading to synthetically challenging materials and processes with negligible commercial scalability. In this thesis, silicon phthalocyanines (SiPcs), synthetically facile molecules most known for their extensive use as dyes and pigments in the industry, were employed as low-cost and scalable active materials for OPV devices. We also report the use of layer-by-layer deposition of the donor and acceptor layer providing a more scalable process compared to the conventional blended heterojunction morphology. Different SiPc derivatives, both soluble and non-soluble, were used as acceptors, paired with different donor polymers (P3HT, PCDTBT, and PBDB-T) and integrated into hybrid evaporation-solution and all-solution layer-by-layer OPV devices. Significant device engineering and optimization was performed through the investigation of several processing conditions such as solvent choice, spin-speed, concentration and annealing temperature/time. In particular, all-solution processed SiPc-based bilayer OPV devices achieved PCEs above 3% with Voc above 1 V, which was similar to performances of corresponding BHJ OPVs. SiPc derivatives also demonstrated their ability to act as electron transport layers in perovskite solar cells. These results further establish the potential of SiPc derivatives as active materials in different solar technologies, while promoting the use of the bilayer structure in OPV devices.

In Canada, many remote communities rely on diesel power for the majority of their energy needs, which can cause negative ecological and health impacts while limiting economic development. Bifacial photovoltaics present an alternative to diesel power. With high average latitudes, these communities show potential for large bifacial gains due to high albedo caused by snow and a high fraction of diffuse light; however, high-latitude conditions deviate from standard test conditions, with low average temperatures, light incident from many directions, and high average air masses, resulting in increased energy yield prediction uncertainty. This thesis describes the performance of bifacial silicon heterojunction cells and modules under high-latitude operating conditions, including high angles of incidence and high air masses. Optical losses in the cell and module are described, and module characteristics are incorporated in DUET, the SUNLAB's energy yield prediction software, as an incidence angle modifier and air mass modifier. The percentage change in energy yield when considering air mass is shown to increase with increasing latitude: for a single-axis-tracked installation, the annual difference in energy yield is 0.5% in a low-latitude location (33°N), and more than 2.5% in a high-latitude location (69°N). Air mass correction is demonstrated to improve energy yield prediction accuracy compared to the absence of spectral correction. This work improves energy yield prediction accuracy for high-latitude locations, facilitating adoption of solar energy in diesel-dependent remote communities in Canada and abroad.

No description available.

The use of Photovoltaic (PV) systems to meet energy demand in rural or remote regions of the world is growing at a very fast pace. Rural electrification projects in developing countries have relied primarily on subsidies from both the government and the national utility. Since using the national grid to meet energy demand in these areas has been found to be quite expensive over time, governments in developing countries have turned to photovoltaic technology as a means of providing electricity needs to their rural population. To facilitate the use of PV systems in developing countries, the author has developed an interactive menu-driven design tool called PVONE that may serve as a guide to engineers and government officials to decide whether a stand-alone photovoltaic system is feasible at a location. PVONE consists of three parts - insolation, system design and economic analysis. In order to predict insolation, PVONE first utilizes the clear sky insolation model that is based on latitude, longitude and altitude of a location. Then it incorporates the standard classification criteria to classify the days of a month according to day types. Based on how the days are classified, a new set of insolation is predicted. For system design, the PVONE program is used to determine the array characteristics based on the chosen photovoltaic module, the system design load and the daily insolation at the location. To determine whether the proposed system is feasible at the location, the PVONE program performs an energy output analysis and economic analysis. The system designed is considered feasible at the location only if it satisfies the load demand and has a positive net present value. / Master of Science

GaSb Thermophotovoltaics are a key technology in the search for the ability to power small scale autonomous systems. In this work, MBE grown GaSb photovoltaic devices are fabricated and tested under AM 1.5 conditions. These devices displayed short circuit current values as high as 40 mA/cm2 but were found to have poor series resistance. The parasitic resistive characteristics were factored out of the measured cell data and it was found that the photocurrent for the fabricated devices could be as much as 6 mA/cm2 higher then the measured short circuit current. An additional layer of metal was added to the reduce the deleterious resistance characteristics, and it was found to lower the series resistance down to a 4 Ω average across almost all of the devices. The average JSC for all of these devices increased to over 30 mA/cm2, with highs well over 40 mA/cm2, a more consistent result than the original single metal deposition devices. Graphene was applied to the originally fabricated devices in an attempt to remove the series resistances issues as well as act as a surface passivation layer. The graphene was able to reduce series resistance by as much as 50% on some of the devices, with a corresponding 6 mA/cm2 increase in short circuit current exhibited. The photocurrent and diode current values were not changed by more than a measurement error, an indication that surface passivaiton may not have taken place. Graphene was a suitable approach for solving the series resistance issue and its use as both a transparent conductive layer and surface passivation material deserve further investigation. / Master of Science

This work focuses on the design, synthesis and characterisation of novel ruthenium bipyridyl complexes and their use in dye sensitised solar cells (DSSCs). Four series of dyes have been synthesised with the general formula Ru(R-bpy)2L, where R = H, CO2Et, CO2H and L represents four different bidentate ligands; cyanodithioimidocarbonate (L1), ethyl xanthate (L2), 2,3-bis(2-cyanoethylthio)-6,7-bis(methylthio) tetrathiafulvalene (L3) and Cu(exoO2-cyclam) (L4). These have been chosen to investigate two key aims: firstly, the increase of the light-harvesting ability of the dye and secondly, the retardation of the recombination of the injected electron with the oxidised dye. Each complex was characterised using electrochemistry, absorption spectroscopy, spectroelectrochemistry and hybrid-DFT calculations. In addition the performance of the acid derivatives in a DSSC was also investigated using IPCE and IV measurements, as well as transient absorption spectroscopy. Two different S-donor ligands, L1 and L2, have been used to investigate the effect of these strongly electron-donating systems on the light-harvesting ability of the dye. Complexes utilising the di-anionic L1 were shown to exhibit significantly increased absorption range and higher extinction co-efficients, relative to the high efficiency dye N719. This dye series also showed a large degree of S-donor ligand character to the HOMO, deduced via spectroelectrochemical and computational studies. Despite these advantageous features the dye performed very poorly in a DSSC, which was attributed to fast recombination. This was a result of the cyano group of L1 coordinating to the TiO2 in addition to the acid groups of the bipyridine ligands. The complexes synthesised with the mono-anionic L2 on the other hand showed only a slightly increased lightharvesting ability relative to N719 and no significant ligand character to the HOMO. However, the performance of this dye in a DSSC was more promising, with efficiencies of up to ~ 2 % achieved. The control of the loss mechanism via recombination of the injected electron with the oxidised dye in a DSSC was investigated by incorporating redox-active ligands, L3 and L4. The series of dyes synthesised with L3 showed significant ligand character to the HOMO orbital, as deduced by spectroelectrochemical, emission and computational studies. Upon adsorption of the acid derivative to TiO2 an extremely long-lived chargeseparated state of 20 ms was observed via transient absorption spectroscopy. Despite this unique long-lived charge-separated state, the dye yielded extremely low DSSC efficiencies. This was attributed to the poor regeneration of the neutral dye by iodide, which in turn was thought to be the result of a stable intermediate formation between the dye cation and the iodide anion. The complexes synthesised with L4 showed the highest light-harvesting efficiency of all the series studied with a wide absorption range and large molar extinction co-efficients. Whilst the maximum efficiency of the dye in a DSSC was nearly 3 %, the performance was found to vary under prolonged irradiation. This was attributed to the degradation of the dye by either exchange of the counter ions with the electrolyte or loss of L4.

An efficient and flexible modelling and simulation toolset for solving spatially-resolved models of photovoltaic (PV) devices is developed, and its application towards a quantitative description of localised electrical behaviour is given. A method for the extraction of local electrical device parameters is developed as a complementary approach to the conventional characterisation techniques based on lumped models to meet the emerging demands of quantitative spatially-resolved characterisation in the PV community. It allows better understanding of the effects of inhomogeneities on performance of PV devices. The simulation tool is named PV-Oriented Nodal Analysis (PVONA). This is achieved by integrating a specifically designed sparse data structure and a graphics processing unit (GPU)-based parallel conjugate gradient algorithm into a PV-oriented numerical solver. It allows more efficient high-resolution spatially-resolved modelling and simulations of PV devices than conventional approaches based on SPICE (Simulation Program with Integrated Circuit Emphasis) tools in terms of computation time and memory usage. In tests, mega-sub-cell level test cases failed in the latest LTSpice version (v4.22) and a PSpice version (v16.6) on desktop PCs with mainstream hardware due to a memory shortage. PVONA efficiently managed to solve the models. Moreover, it required up to only 5% of the time comparing the two SPICE counterparts. This allows the investigation of inhomogeneities and fault mechanisms in PV devices with high resolution on common computing platforms. The PVONA-based spatially-resolved modelling and simulation is used in various purposes. As an example, it is utilised to evaluate the impacts of nonuniform illumination profiles in a concentrator PV unit. A joint optical and electrical modelling framework is presented. Simulation results suggest that uncertainties introduced during the manufacturing and assembly of the optical components can significantly affect the performance of the system in terms of local voltage and current distribution and global current-voltage characteristics. Significant series resistance and shunt resistance effects are found to be caused by non-uniformity irradiance profiles and design parameters of PV cells. The potential of utilising PVONA as a quality assessment tool for system design is discussed. To achieve quantitative characterisation, the PVONA toolset is then used for developing a 2-D iterative method for the extraction of local electrical parameters of spatially-resolved models of thin-film devices. The method employs PVONA to implement 2-D fitting to reproduce the lateral variations in electroluminescence (EL) images, and to match the dark current-voltage characteristic simultaneously to compensate the calibration factor in EL characterisations. It managed to separate the lateral resistance from the overall series resistance effects. The method is verified by simulations. Experimental results show that pixellation of EL images can be achieved. Effects of local shunts are accurately reproduced by a fitting algorithm. The outcomes of this thesis provide valuable tools that can be used as a complementary means of performance evaluation of PV devices. After proper optimisation, these tools can be used to assist various analysis tasks during the whole lifecycle of PV products.