An in-depth study of concentration gradients in thermally-interdiffused polymer – fullerene photovoltaic devices, with a focus on thickness and heat treatments, is presented in this thesis. Device performance is improved from the bilayer by the creation of a concentration gradient of the donor and acceptor materials throughout the active layer of the device. Concentration gradients are expected to improve device performance by optimizing the charge transfer, transport and collection processes. This is achieved through heat-induced interdiffusion of the two materials at temperatures above the glass transition temperature of the polymer. Investigation of the poly(3-octylthiophene) (P3OT) – C₆₀ system show a three-fold improvement in the external quantum efficiencies (EQE) as compared with bilayer devices. Auger spectroscopy, combined with argon-ion beam milling, serves to record the concentration depth profile and identify concentration gradients in the device through detection of the sulfur in the P3OT backbone. Concentration gradients are optimized to yield the best devices through a thickness variation study conducted on the P3OT – C₆₀ system for fixed thermal interdiffusion conditions at 118 °C for 5 minutes. An optimum thickness of 40 to 60 nm is obtained for the two materials that yields the ideal morphology of a concentration gradient as recorded by Auger spectroscopy. For such devices, the concentration gradient is seen to extend through the device, ending in a thin layer of pure material at each electrode. A monochromatic power conversion efficiency of 2.05% is obtained for 5.3 mW/cm²⁺ illumination at 470 nm. A brief study is also presented to optimize the concentration gradient profile through variations of the thermal parameters. The dependence of the concentration gradient on the interdiffusion time and temperature is investigated. The merits of heat treatment on the crystallinity of P3OT and the overall device performance are also discussed. It is shown in some case that devices with annealed P3OT layers show almost twice the EQE as non-annealed P3OT layer devices. Potential alternatives for C₆₀ in interdiffused devices with P3OT have been presented. [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), a well-investigated acceptor for blend devices, is studied as an acceptor in concentration gradient devices. A method for spin-coating uniform bilayers of P3OT and PCBM, without solution damage to either layer, is presented. A thermal variation study of the interdiffusion conditions on this system indicated higher interdiffusion temperatures and times are preferred for P3OT – PCBM systems. For interdiffusion at 150 °C for ten minutes, EQE values approaching 35 % at 500 nm are obtained. Auger spectroscopy studies on this system yielded the same conclusions about the concentration gradient device morphology that gives optimum device output. 1:1 and 1:2 blends of P3OT – PCBM are also studied. The influence of various thermal treatments on these devices is described. The endohedral fullerene Sc₃N@C₈₀ is introduced as a new acceptor material. The endohedral fullerene consists of Sc₃N cluster enclosed in a C₈₀ cage. An order of magnitude increase is seen in device performance upon sublimation of these molecules on a P3OT layer confirming its effectiveness as an acceptor. Preliminary studies done on this system indicated the need for greater thermal treatment to produce optimum concentration gradients. An in depth study for varying temperatures and times is presented. The best device performance was seen for interdiffusion at 160 °C for 25 minutes. The endohedral fullerene devices also show a long-term deterioration and so best result are presented from a set of devices fabricated within the same time period. The study of these three donor-acceptor systems confirms that the conclusions on the thickness dependence and device performance study conducted for the P3OT – C₆₀ system extend to other acceptors. A model of EQE for varying thicknesses based on absorption in the interdiffused concentration gradient regions is also presented. This model effectively highlights the influence of P3OT layer thickness on the trends observed in the EQE. It did not, however, reproduce the experimental thickness variation results for varying C₆₀ thicknesses. Incorporation of the effects of the electric field intensity distribution is expected to correct for this. Suggestions have been given on how this might be achieved. / Ph. D.

Photovoltaic (PV) technologies are a promising approach to achieve clean, renewable energy production on a global scale. However, the widespread implementation of this technology is limited due to the intricate challenges associated with its complex electrochemical processes. One such challenge is the formation of long-lived charge-separated states (CSSs), a process that directly influences device efficiencies. Viable strategies for increasing CSS lifetimes involve the inhibition of parasitic back-electron transfer pathways. In liquid-junction PVs, electronic recombination is prevented by utilizing redox electrolytes that promote directional electron transfer at the electrode/electrolyte interface, where forward electron transfer (i.e. to the electrode) is favored and the corresponding electronic recombination reaction is impeded. To meet this criterion, researchers seek to employ redox electrolytes that undergo a spin-exchange reaction induced by electron transfer. This event, known as charge transfer-induced spin crossover (CTISC), significantly increases the reorganization energy associated with electronic recombination, producing long-lived CSSs and elevated device efficiency. This dissertation describes a suite of manganese-based redox mediators that exhibit CTISC across a tunable range (1.5 V) of formal potentials (E1/2). These complexes are utilized as redox electrolytes in liquid-junction PVs and result in a two-fold enhancement in the device efficiency relative to other CTISC redox species. Photosensitizer regeneration rates are monitored using transient absorption spectroscopy (TAS) to discern the optimal E1/2 values in this class of complexes while density functional theory is employed to calculate the reorganization energy of each species. By implementing these promising electrolytes into PV devices, scientists and engineers are armed with new tools to increase the accessibility and efficiency of next-generation PVs, thereby transforming past promises into progress. / Doctor of Philosophy / To realize next-generation renewable fuels, scientists must understand how electron transfer at an interface is controlled. This dissertation highlights one method of forming a chemically useful and long-lived charge separated state. The formation of this charge separated state is achieved through an electronic reorganization that occurs at a metal center after electron transfer. Chapters 2, 3, and 4 investigate the synthesis and characterization of new metal species that possess this electronic reorganization process and provide an advanced understanding of how this process facilitates the formation of long-lived charge separated states. This work is intended to motivate new schools of thought that aid the design of next-generation catalytic materials for light-driven chemical reactions.

This diploma thesis deals with the design of a photovoltaic power plant with a battery storage for a family house. In the theoretical part at first the principle of photovoltaic cells is analysed together with the various types used in this branch. Furthermore, the thesis deals with the description of photovoltaic systems and its individual parts consisting of inverters and accumulators. This thesis analyses the object for the installation of a photovoltaic power plant, including legislative and subsidy conditions. In the final part, itself system is analysed with a price proposal.

This diploma thesis deals with the design of a photovoltaic solar power station for a specific family house in the Jihlava region. The aim of the work was to get acquainted with technologies about the production of solar systems, evaluate the market in the Czech Republic and create a design of photovoltaic solar power station. Three designs of power stations were created with the help of the PV * SOL design system. Each design uses different photovoltaic cell technology. The result of each power station design is a complete finished project, which is based on many factors such as the efficiency of the entire system in a certain location, financial analysis, return on investment and more. In addition, these projects meet the conditions for the preparation of the subsidy program Nová zelená úsporám. At the end of the work, all three designed power stations are evaluated and with the help of multicriteria analysis, the best and most advantageous power station design for the given locality is determined. In the end, the idea of further development of the project is presented.

The ongoing energy transition in Germany foresees significant increases in the share of renewable energies in the country’s electricity mix until 2030. A share of 80% is targeted and photovoltaics should have a major contribution with a total capacity of 215 Gigawatts aimed to be installed. Since the beginning of the energy transition in Germany, the Renewable Energy Sources Act (EEG) has played a key role with its regulations and support measures. The latest amendment of the EEG in January 2023 includes updated capacity addition targets and regulatory measures. In recent years, the solar branch in Germany has experienced growth after a period of drought from 2013 to 2017. The governmental plans are the basis to enable further growth, but challenges and uncertainties remain if the targets can be reached under the present and anticipated future constraints. This paper presents an evaluation of the feasibility of the capacity addition targets for photovoltaics and outlines the potential contribution of different photovoltaics system types within the installation plans. Through the conduction of semi-structured interviews with different stakeholders of the solar branch in Germany, a large variety of knowledge, experiences, perspectives and assessments is combined to theory which provides answers to the research questions. The results of the data analyses show, that the governmental targets are theoretically feasible but it is doubtful whether they will be reached in practice. Two of the main challenges which will need to be overcome are lacking installation capacities in form of skilled workers and hindering bureaucratic processes regarding planning, approvals, operations and accounting of photovoltaics plants. Moreover, the results indicate that the share of large-scale systems should increase, as scale-effects make them more cost-efficient and more capacity can be installed in the same amount of time. Most of these systems will be ground-mounted, but industrial roof-top systems will also contribute to a certain extent. Furthermore, integrated photovoltaic applications will increase in importance, due to the scarcity of areas and potential synergies. However, most of the stakeholders do not see a major contribution of such systems until 2030, as costs are too high, specific regulations are missing and market awareness is still low. Despite the dominance of large-scale systems, the segment of residential roof-top photovoltaic systems also has a high potential and consumers will want to produce their own electricity due to high energy prices and supply uncertainties.

No description available.

In the recent years area organic photovoltaics is generating a lot of interests because whole process of synthesis and fabrication is less energy intensive process as well as it is cost effective compared to conventional inorganic Si based photovoltaic technology. This work mainly deals with the fabrication and optimization of device fabrication conditions for organic photovoltaic materials. In first part of the work, the solar cell fabrication conditions were optimized for the commonly used system P3HT – PCBM. The fabricated device was optimized for the solvents used for the active material, concentration of the active material solution, donor- acceptor ratio of the active material, annealing conditions of the active layer and the metal evaporation conditions for the cathode. All the optimization procedures were carried out in controlled atmosphere to minimize the environmental effect inference during fabrication of the solar cell devices. All the characterization was carried out at ambient conditions. The efficiency of the solar cell was improved from 0.009% to 6.2%. the environmental stability of the fabricated devices were carried out after encapsulating it with epoxy based resin in both ambient conditions as well as extreme conditions like 85% RH at 25°C inside the humidity chamber. It was observed that both the data matches well with each other indicating proper encapsulation required to safe guard the device for the better performance over the period of time. Second part of this work mainly deals with understanding the structure property relationship of thiophene based donor- acceptor- donor molecule 2,5-dithienyl-3,4-(1,8-naphthylene) cyclopentadienone (DTCPA), which is highly crystalline, low band gap organic molecule which absorbs over entire visible region of the solar spectra. DTCPA crystals of various morphologies were prepared by various recrystallization routes. It was observed that macro scale morphology of these crystals differs from each other. Also depending on the method of recrystallization sizes of the crystals also varies. All the recrystallized DTCPA shows strong orientation toward (001) direction. However, it was observed that lattice parameters of these crystals slightly differ from each other owing to the recrystallization methodology. These variations in crystal parameters are more than 0.02 which is significant. It was also observed that the crystallite sizes depend on the recrystallization routes. Slow evaporation of concentrated solution (SEC) grown crystals has the larger crystallite size of 170nm. It was observed that absorption range of these crystals slightly differ from each other owing to the change in the crystallite sizes and crystal parameters. Third part of this work deals with the fabrication and optimization of thermal evaporation process of DTCPA for photovoltaic applications. DTCPA is stable at higher temperatures as well as has sharp melting point which make it ideal candidate for thermal evaporation. In this work films of DTCPA were fabricated for various evaporation rates by thermal evaporation technique. Chemical integrity of the molecules upon evaporation is found to be intact as observed from FTIR spectroscopy. XRD shows that at lower (25 W/m2) as well as higher (40 W/m2) films are oriented to (001), (400) as well as (311) directions, at 30 W/m2 and 35 W/m2 there is a strong orientation towards (311) and (001) directions respectively. Photo luminescence studies indicate that there is strong 410 nm emission for films deposited at the power of 25 W/m2 and 40 W/m2. Microscopic studies confirm that morphology is dependent on the deposition rates as it changes with the change in deposition rate. This in turn reflects in the device characteristics of these films. It was observed that films deposited at high deposition rates show better device characteristics with high VOC and current density values. All these device fabrication and characterizations were carried out in ambient conditions. Fourth part of this work deals with P3HT - DTCPA composites which exhibit wide range of light absorption. It was observed that DTCPA act as nucleating centers for the P3HT molecules and increases crystallinity in the composite. Furthermore, DTCPA helps in exciton separation because of donor and acceptor moieties present in the molecule. It also helps in charge transportation because of its crystalline nature and further it induces molecular ordering in the P3HT matrix. The band diagram of P3HT- DTCPA suggests that the band edges of both materials are ideal for charge separation. In addition, crystalline nature of the DTCPA molecule helps in effective charge transportation. J-V characteristics shows that there is large built in potential in the devices from these blends leading to large Voc. Composites with lower DTCPA loadings show higher efficiency than with higher loadings. These devices were prepared in ambient conditions and needs to be optimized for obtaining better device properties. In the fifth part of the work two types of system were studied to understand the band edge matching on the photovoltaic properties, carbazole based copolymers and DTCPA based copolymers. In the case of carbazole based copolymers it was observed that by copolymerizing carbazole with thiophene based derivatives lowers the band gap and modifies the HOMO and LUMO levels for better suit for the photovoltaic device fabrication. It was observed that that is two orders of improvements in the efficiency by co polymerizing carbazole with benzothiodizole as improves the JSC and VOC. Also the copolymerization of carbazole with both benzothiodiazole and bithiophene results in better light harvesting as the optical band gap was lowered. In the case of DTCPA copolymers with DTBT and DHTBT as both are random copolymers the solubility was low as well as their HOMO band edge was mismatched with the PEDOT: PSS which is a hole transport layer. However, the alternate polymerization of DTCPA with DTBT improved the band edge matching and also the solubility. As a result there was tenfold improvement in the charge collection and hence the efficiency was improved from 0.02% to 2.4%. Many of the conducting polymers have good material property but poor filmability. In the sixth part of this work deals with fabrication of device quality films by alternate deposition technique like pulsed laser deposition. Two types of system were studied in this work (i) polypyrrole- MWCNT nanocomposites and (ii) Poly DTCPA polymer. In both the cases it was observed that chemical integrity of the polymer retained during ablation. PolyDTCPA films were fabricated by pulsed laser deposition by both IR (Nd-YAG) and UV (KrF) laser source. Morphological studies indicate that IR laser ablated films were particulate in nature whereas UV laser ablated films were grown as continuous layers as polyDTCPA absorbs better in UV region. As a result the IV characteristics indicate that IR laser ablated films are resistive in nature and UV laser ablated films are good rectifiers indicating the suitability of the process for fabrication of device quality films.

Global economic trends suggest that there is a need to generate sustainable renewable energy to meet growing global energy demands. Solar energy harnessed by concentrated photovoltaic (CPV) systems has a potential for strong contributions to future energy supplies. However, as a relatively new technology, there is still a need for considerable research into the relationship between the technology and the solar resource. Research into CPV systems was carried out at the University of Ottawa’s Solar Cells and Nanostructured Device Laboratory (SUNLAB), focusing on the acquisition and assessment of meteorological and local solar resource datasets as inputs to more complex system (cell) models for energy yield assessment. An algorithm aimed at estimating the spectral profile of direct normal irradiance (DNI) was created. The algorithm was designed to use easily sourced low resolution meteorological datasets, temporal band pass filter measurement and an atmospheric radiative transfer model to determine a location specific solar spectrum. Its core design involved the use of an optical depth parameterization algorithm based on a published objective regression algorithm. Initial results showed a spectral agreement that corresponds to 0.56% photo-current difference in a modeled CPV cell when compared to measured spectrum. The common procedures and datasets used for long term CPV energy yield assessment was investigated. The aim was to quantitatively de-convolute various factors, especially meteorological factors responsible for error bias in CPV energy yield evaluation. Over the time period from June 2011 to August 2012, the analysis found that neglecting spectral variations resulted in a ~2% overestimation of energy yields. It was shown that clouds have the dominant impact on CPV energy yields, at the 60% level.

Global economic trends suggest that there is a need to generate sustainable renewable energy to meet growing global energy demands. Solar energy harnessed by concentrated photovoltaic (CPV) systems has a potential for strong contributions to future energy supplies. However, as a relatively new technology, there is still a need for considerable research into the relationship between the technology and the solar resource. Research into CPV systems was carried out at the University of Ottawa’s Solar Cells and Nanostructured Device Laboratory (SUNLAB), focusing on the acquisition and assessment of meteorological and local solar resource datasets as inputs to more complex system (cell) models for energy yield assessment. An algorithm aimed at estimating the spectral profile of direct normal irradiance (DNI) was created. The algorithm was designed to use easily sourced low resolution meteorological datasets, temporal band pass filter measurement and an atmospheric radiative transfer model to determine a location specific solar spectrum. Its core design involved the use of an optical depth parameterization algorithm based on a published objective regression algorithm. Initial results showed a spectral agreement that corresponds to 0.56% photo-current difference in a modeled CPV cell when compared to measured spectrum. The common procedures and datasets used for long term CPV energy yield assessment was investigated. The aim was to quantitatively de-convolute various factors, especially meteorological factors responsible for error bias in CPV energy yield evaluation. Over the time period from June 2011 to August 2012, the analysis found that neglecting spectral variations resulted in a ~2% overestimation of energy yields. It was shown that clouds have the dominant impact on CPV energy yields, at the 60% level.

The description of a novel device to measure the spectral direct normal irradiance is presented. The solar spectral irradiance meter (SSIM) was designed at the University of Ottawa as a cost-effective alternative to a prohibitively expensive field spectroradiometer (FSR). The latter measures highly-varying and location-dependent solar spectrum, which is essential for accurate characterization of a concentrating photovoltaic system’s performance. The SSIM measures solar spectral irradiance in several narrow wavelength bands with a combination of photodiodes with integrated interference filters. This device performs spectral measurements at a fraction of the cost of a FSR, but additional post-processing is required to deduce the solar spectrum. The model was developed to take the SSIM’s inputs and reconstruct the solar spectrum in 280–4000 nm range. It resolves major atmospheric processes, such as air mass changes, Rayleigh scattering, aerosol extinction, ozone and water vapour absorptions. The SSIM was installed at the University of Ottawa’s CPV testing facility in September, 2013. The device gathered six months of data from October, 2013 to March, 2014. The mean difference between the SSIM and the Eppley pyrheliometer was within ±1.5% for cloudless periods in October, 2013. However, interference filter degradation and condensation negatively affected the performance of the SSIM. Future design changes will improve the longterm reliability of the next generation SSIMs.