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<p><p lang="en-US">This experimental research thesis describes the combination of conjugated polymers and carbon nanotubes with the fields of electrophoretic deposition (EPD) and organic solar cells. Prior to these contributions, soluble conjugated polymers and carbon nanotubes that have been functionalized by them had not yet been deposited by EPD from solution or by using non-toxic solvents. Additionally, EPD had not yet been utilized to deposit the active layer in a solid organic photovoltaic device. <p lang="en-US">The EPD of soluble conjugated polymer functionalized carbon nanotubes from non-toxic solvents was achieved through an iterative process of experimentation and technique refinement. The developed EPD technique utilized the high pH region at the cathode substrate to neutralize positively charged weak polyelectrolytes macromolecules. Their functional groups were protonated using a minimized amount of acetic acid which also enabled their solubility. Deprotonation of the quaternary ammonium functional groups rendered them neutrally charged and insoluble tertiary amines. This mechanism facilitated the formation of coatings that were predictable and uniform in appearance and thickness. <p lang="en-US">Control over coating thickness was demonstrated by coatings spanning 100 nm to 10 μm. These coatings were produced by adjusting the applied voltage, solution concentration, and tuning the deposition duration. <p lang="en-US">Techniques for the fabrication of a photovoltaic device using an active layer produced by EPD were established though modifications of general organic photovoltaic device fabrication procedures. These modifications involved redesigning the photolithographic ITO etching pattern, adding an insulating barrier strip, thickening the aluminum electrode layer, and switching the top buffer layer from LiF to BCP.</p> / Master of Applied Science (MASc)

Achieving high efficiency solar cells and concurrently driving down the cell cost has been among the key objectives for photovoltaic researchers to attain a lower levelized cost of energy (LCOE). While the performance of silicon (Si) based solar cells have almost saturated at an efficiency of ~25%, III-V compound semiconductor based solar cells have steadily shown performance improvement at approximately 1% (absolute) increase per year, with a recent record efficiency of 46%. However, the expensive cost has made it challenging for the high efficiency III-V solar cells to compete with the mainstream Si technology. Novel approaches to lower down the cost per watt for III-V solar cells will position them to be among the key contenders in the renewable energy sector. Integration of such high-efficiency III-V multijunction solar cells on significantly cheaper and large area Si substrate has the potential to address the future LCOE roadmaps by unifying the high-efficiency merits of III-V materials with low-cost and abundance of Si. However, the 4% lattice mismatch, thermal mismatch polar-on-nonpolar epitaxy makes the direct growth of GaAs on Si challenging, rendering the metamorphic cell sensitive to dislocations. The focus of this dissertation is to systematically investigate heterogeneously integrated III-V multijunction solar cells on Si substrate. Utilizing a combination of comprehensive solar cell modeling and experimental techniques, we seek to better understand the material properties and correlate them to improve the device performance, with simulation providing a very valuable feedback loop. Key technical design considerations and optimal performance projections are discussed for integrating metamorphic III-V multijunction solar cells on Si substrates for 1-sun and concentrated photovoltaics. Key factors limiting the “GaAs-on-Si” cell performance are identified, and novel approaches focused on minimizing threading dislocation density are discussed. Finally, we discuss a novel epitaxial growth path utilizing high-quality and thin epitaxial Ge layers directly grown on Si substrate to create virtual “Ge-on-Si” substrate for III-V-on-Si multijunction photovoltaics. With the plummeting price of Si solar cells accompanied with the tremendous headroom available for improving the III-V solar cell efficiencies, the future prospects for successful integration of III-V solar cell technology with Si substrate looks very promising to unlock an era of next generation of high-efficiency and low-cost photovoltaics. / Ph. D.

Semiconducting polymers are promising materials for next-generation, flexible electronics devices. Over the last decades, various types of polymers have been developed and applied to devices such as light-emitting diodes (OLEDs), photovoltaics (OPVs), and field-effect transistors (OFETs). Conductivity is one of the most important parameters for the device performance since it directly affects charge carrier collection, injection, and transport. Besides, not only bulk conductivity but also interfacial energy barrier is critical for multilayer devices, especially an energy alignment of layers is essential to collect/inject charge carriers smoothly. Therefore reliable systems for both p- and n-type doping are sought after. Chemical doping (molecular doping) is a promising technique to achieve both, to enhance the conductivity in polymers and to shift energy levels by generating charge carriers (holes or electrons) in polymer films. The method enables to transport charge carriers in thin films or between neighboring layers effectively. This thesis investigates the chemical doping from the nanostructure level, particularly two types of devices where doping plays a crucial role: 1) pressure sensor based on p-doped semiconducting polymer nanopillars, 2) novel n-type doping system for a technologically advantageous thick interlayer in organic solar cells. In the first part, an application of nanostructured p-doped polymer was explored in a new type of device. While p-type doping is relatively common, especially for P3HT or PEDOT:PSS, in OPVs or OFETs, the potential of semiconducting polymer material, especially its mechanical flexibility and high electrical conductivity, is not fully utilized in these types of devices. Therefore new electronic device, a pressure sensor, is fabricated based on nanopillar structures made of p-doped P3HT by a templating method. The highly flexible and conductive nanostructure was obtained by combining templating and chemical doping. Through utilizing the buckling behavior of nanopillars, the pressure sensor was constructed and used for the detection of finger movement and touch sensing with a robotic gripper. Besides, the templating process can be tuned by annealing conditions, that enable adjusting the length of nanopillars and thus sensing properties. Finally, the sensing mechanism was investigated by finite element modeling and Euler buckling theory. In the second part, n-type doping in novel polymers was investigated. Generally, n-type doping has relatively limited reports since the n-doped state of commonly used polymers is readily oxidized by oxygen or water in air. A newly synthesized series of naphthalene diimide (NDI)-based conjugated polyelectrolytes (CPEs) contains cations in side chains, which stabilize the generated charge carriers. The stability of conductivity, spectroscopic characteristics, morphology, and the application of CPEs to interlayers in polymer solar cells (PSCs) were investigated. The polymer film showed air-stable high conductivity by introducing self-compensation doping and anion doping methods. The LUMO level of CPEs has a strong correlation with the conductivity in air and long-term stability. Moreover, the work function of the ITO cathode can be shifted by CPEs and the chemical doping, enabling a highly conductive, thick cathode interlayer, applicable to scalable film deposition methods, e.g., the blade-coating method. For the outlook, various new applications can be realized by combining these techniques and materials for p-/n-doping systems. This research expands the utilization of semiconducting polymer as a nano-structurable, flexible, highly conductive, and air-stable component for future flexible electronics devices.

Denna studie har undersökt hur små och stora svenska solcellsföretag budgeterar i osäkra miljöer. Fokus har varit på att jämföra företagen och identifiera likheter och skillnader mellan hur de budgeterar. För att ta fram kunskap i ämnet intervjuades två små solcellsföretag (Solivo AB och Wettersol AB) samt ett stort solcellsföretag (Sesol AB). Resultaten från intervjuerna visar att små solcellsföretag använder en mer informell hantering av budgetering, ofta baserad på magkänsla istället för formella budgetar. Detta på grund av begränsade resurser och tid. De fokuserar på kortfristig planering med täta uppföljningar av kostnader och intäkter, och gör månatliga prognoser för att försäkra att fasta kostnader täcks. Utöver det har de små organisationerna inte samma krav på formella budgetar från ägare och styrelse som stora företag. Stora solcellsföretag, å andra sidan, använder mer avancerade budgetmodeller och styrsystem som faciliterar både långsiktig och kortsiktig planering, med regelbundna månadsvisa uppdateringar. De utnyttjar “Business Intelligence” verktyg för djupgående analys av företaget, vilket ger en bättre förståelse för helheten. Stora företag har också centraliserade kostnadsavdelningar för kostnadskontroll och projektledning. Krav från externa ägare på finansiell rapportering leder till utvecklade ekonomistyrningssystem och mer detaljerade budgetprocesser. På grund av omfattande finansiell planering är stora verksamheter bättre rustade och mer motståndskraftiga mot marknadsfluktuationer vilket kan ge dem en konkurrensfördel.  Trots dessa skillnader påtalar både små och stora företag flera likheter gällande budgetering i en osäker miljö. Båda påvisar vikten av nyckeltal för att mäta prestationer och jämföra med historisk data. Både de små och stora solcellsföretagen använder sig av “top-down-styrning” som styrstruktur, vilket anses effektivt i osäkra miljöer. Dessutom är tät uppföljning och kontinuerliga uppdateringar av budgetarna gemensamma strategier för att anpassa sig till förändringar. / The aim of this study was to examine how two small and one large Swedish solar cell companies use budgeting in uncertain environments. The focus of the study has been on comparing the organisations and to identify their similarities and differences in how they use budgets. In order to do this two small solar cell companies (Solivo AB and Wettersol AB) and one large solar cell company (Sesol AB) were interviewed. The results from the interviews show that small solar cell companies use a more informal budgeting system, often based on gut feeling instead of formal budgets. This is due to a limit of time and resources. Instead they focus on short term planning and regular follow-ups of costs and revenues, and do monthly forecasts to ensure fixed costs are covered. In addition, the small companies do not have the same requirement on formal budgets from owner and board as large companies do. Large solar cell companies, on the other hand, use more advanced budgetary models and control systems that facilitate both long-term and short-term planning, with regular monthly updates. They also use “Business intelligence” tools for thorough analysis of the company, providing a better understanding of the overall picture. Large companies have also centralized cost departments for cost control and project management. External owners’ demands for financial reporting lead to the development of financial management systems and more detailed budget processes. Due to extensive financial planning, large companies are better equipped and more resilient to market fluctuations, potentially giving them a competitive advantage.  Despite these differences, both small and large enterprises highlight multiple similarities regarding budgeting in uncertainty. Both emphasize the importance of key performance indicators to measure performance and compare it with historical data. Both small and large solar cell corporations use top-down management as a governance structure, which is considered beneficial in uncertain environments. Furthermore, close monitoring and continuous updates of budgets are common strategies to adapt to changes.

[pt] A geração de energia fotovoltaica cresceu rapidamente em todo o mundo e está começando a contribuir com uma quantidade notável de produção de eletricidade no cenário mundial. Para desenvolver ainda mais o mercado fotovoltaico (FV), atrair mais empresas investidoras e torná-lo mais competitivo, os custos de produção ainda precisam ser reduzidos e a eficiência das células solares aumentada. Entre todas as tecnologias FV, as células solares de filme fino baseadas em materiais III-V são a tecnologia de maior sucesso e mais promissora para alcançar as mais altas eficiências de conversão de energia. Mesmo com a camada ativa na ordem de micrometros os fotovoltaicos de filmes finos são produzidos sobre substratos rígidos caros, mas indispensáveis como base cristalográfica e suporte mecânico na produção da camada ativa monocristalina. Entretanto, após a obtenção do filme fino FV o substrato original é totalmente dispensável pois não exerce nenhuma funcionalidade na célula. Desta forma, é crescente o interesse por tecnologias que permitam a comercialização de células solares sobre substratos leves, flexíveis e de baixo custo, ampliando não só a gama de aplicabilidades, mas também diminuindo os custos de produção, transporte e instalação. Este trabalho mostrará o desenvolvimento de uma metodologia geral para o processo de transferência de estruturas simples de filmes finos e estruturas de células solares completas de materiais III-V crescidos epitaxialmente por MOVPE (Metal Organic Vapour Phase Epitaxy). Materiais III-V foram transferidos para diferentes bases flexíveis e amostras contendo células solares III-V completas foram transferidas para substrato flexível de cobre obtido por eletrodeposição e para fita adesiva de cobre. As transferências foram realizadas com sucesso, sem danificar a estrutura e os contatos elétricos das células. Medidas de corrente tensão realizadas com simulador solar Sciencetech SF300A, com filtro AM1.5G, mostraram que as células em substratos flexíveis quando comparadas com elas em substratos rígidos apresentaram poucas alterações nas figuras de mérito e eficiência de conversão. As bases testadas apresentaram aderência, flexibilidade e suporte mecânico esperados para os filmes finos testados e as células solares completas transferidas. / [en] Photovoltaic power generation has grown rapidly across the world and is starting to contribute a remarkable amount of electricity production on the world stage. To further develop the photovoltaic (PV) market, attract more investing companies and make it more competitive, production costs still need to be reduced and the efficiency of solar cells increased. Among all PV technologies, thin film solar cells based on III-V materials are the most successful and most promising technology to achieve the highest energy conversion efficiencies. Even with the active layer in the order of micrometers, thin film photovoltaics are produced on expensive rigid substrates, but indispensable as a crystallographic base and mechanical support in the production of the monocrystalline active layer. However, after obtaining the FV thin film, the original substrate is completely unnecessary, since it does not exert any functionality in the cell. In this way, there is a growing interest in technologies that allow the commercialization of solar cells on light, flexible and low-cost substrates, expanding not only the range of applicability, but also reducing production, transport and installation costs. This work will show the development of a general methodology for the transfer process of simple thin-film structures and complete solar cell structures of III-V materials epitaxially grown by MOVPE (Metal Organic Vapour Phase Epitaxy). III-V materials were transferred to different flexible bases and samples containing complete III-V solar cells were transferred to flexible copper substrate obtained by electrodeposition and to copper adhesive tape. The transfers were carried out successfully, without damaging the structure or the electrical contacts of the cells. Current voltage measurements, performed with a Sciencetech SF300A solar simulator, with AM1.5G filter, showed that cells on the flexible substrates, when compared to them on rigid substrates, showed little changes in their figures of merit. The bases tested showed adhesion, flexibility and mechanical support expected for the thin films and complete solar cells transferred.

Six peripherally meso-modified Zn (II) porphyrin sensitizer dyes are designed and their J-V performance in dye sensitized solar cell (DSSC) evaluated. Electron-donating groups including phenothiazine, carbazole and pyrene are used to modify the porphyrin macrocycle at the meso-carbon position(s). To compare the effect of donor substitution on the performance of the cells in terms of short circuit current (Jsc), light harvesting efficiency (LHE) and power conversion efficiency (η), two sets of sensitizers with different degrees of substitution are synthesized. One set of dyes (mono-substituted) have one electron donor at trans-position to the acceptor, while the second set (tri-substituted) dyes have three of the same type electron donor groups at 5, 10 and 15 meso-carbon positions making all the six dyes push-pull type sensitizers incorporating 4'-carboxyphenyl as an electron-acceptor/anchor group. Different spectroscopic and electrochemical methods are used to study the photophysical and electrochemical properties of the dyes, while the photovoltaic performance of their cells under 1.5 A.M is studied using solar simulator. Meso-substitution of Zinc (II) porphyrin with these small donor molecules is shown to improve the light harvesting character of the Zinc (II) porphyrin macrocycle in the UV-Vis absorption while at same time improving its fluorescence quantum yield, excited-state life time and electron donating potential. All these factors combined make these meso-modified dyes better sensitizers with suitable Δ0 Δ0, and much improved power conversion efficiencies (PCE) compared to unsubstituted Zn (II) porphyrin. In particular, as a result of the peripheral modification, a doubling in efficiency in the mono- substituted series (RA-200-Zn; η=^M 4.2%, Jsc= -13.13 mA cm-2, Voc=0.54 ) and tripling in the tri-substituted series ( tri-phenothiazine Zn (II) Porphyrin; η= 7.3%, Jsc= -18.15 mA cm-2, Voc= 0.55 ) compared to unsubstituted Zn (II) porphyrin (η= 2.11%, Jsc= -5.7 mA cm-2, Voc= 0.53 V) has been accomplished.

The aim of the work is to create a coherent overview of the silicon monocrystaline solar cell in terms of the physical principle of the structure and sequence of technological operations necessary for its production. The effect of individual manufacturing steps is discussed in relation to the requirement of decreasing recombination, optical and ohmic losses of the monocrystalline solar cell. Due to a theoretical assumption, one-dimensional model of solar cell was created in a PC1D software that was later optimized to achieve the highest possible efficiency. Using the available technologies, final model of the solar cell is manufactured in Solartec company and in the end of the work compared with the output of simulation.