Most of the photovoltaic (solar cell) systems in Sweden today are installed on private houses and connected to the public grid. Photovoltaic (PV) power can be consumed directly in the house, called self-consumption, or fed in to the public grid. For the house owner self-consumed PV energy often has a higher economic value than sold excess PV energy, since the savings from not buying one kWh is larger than the income of selling one kWh. The self-consumption can be expressed as an absolute value; amount of produced/consumed kWh, or as a relative; absolute self-consumption divided with total PV production. The PV production and self-consumption were calculated on an hourly basis. In this Master thesis a MATLAB tool for calculating and optimizing the production, absolute and relative self-consumption and profit for PV systems with panels in one (1DPV), two or three directions (3DPV) was developed. The results show possibilities to increase especially the relative self-consumption with 3DPV. There is however no economic gain of using 3DPV instead of south-directed 1DPV for the studied case; a private house close to Västerås with a 1DPV system of 3360 W and variable electricity prices based on hourly Nord Pool Spot prices. The rated power of the inverter can be decreased with 3DPV compared to south-oriented 1DPV and still keep minimal production losses. A smaller inverter and other peripheral equipment such as cables might compensate for the lower yearly profit with 3DPV when calculating the payback period. Further studies of economic aspects and how to optimize them have to be carried out for 3DPV systems, since economy is very crucial for investment decisions.

The development of organic photovoltaics (OPVs) has attracted a lot of attention due to their potential to create a low cost flexible solar cell platform. In general, an OPV is comprised of a number of layers of thin films that include the electrodes, active layers and barrier films. Thus, with all of the interfaces within OPV devices, the potential for failure exists in numerous locations if adhesion at the interface between layers is inherently low or if a loss of adhesion due to device aging is encountered. To date, few studies have focused on the basic properties of adhesion in organic photovoltaics and its implications on device reliability. In this dissertation, we investigated the adhesion between interfaces for a model multilayer barrier film (SiNx/PMMA) used to encapsulate OPVs. The barrier films were manufactured using plasma enhanced chemical vapor deposition (PECVD) and the interfacial fracture toughness (Gc, J/m2) between the SiNx and PMMA were quantified. The fundamentals of the adhesion at these interfaces and methods to increase the adhesion were investigated. In addition, we investigated the adhesive/cohesive behavior of inverted OPVs with different electrode materials and interface treatments. Inverted OPVs were fabricated incorporating different interface modification techniques to understand their impact on adhesion determined through the interfacial fracture toughness (Gc, J/m2). Overall, the goal of this study is to quantify the adhesion at typical interfaces used in inverted OPVs and barrier films, to understand methods that influence the adhesion, and to determine methods to improve the adhesion for the long term mechanical reliability of OPV devices.

Mindre än en timmes solsken på vår planet innehåller mer energi än hela världens energiförbrukning på ett helt år. Ett vanligt villatak i Sverige tar på ett år emot flera gånger mer energi än vad dess behov är. Potentialen för solenergi är mycket stor. Samtidigt använder samhället idag stora mängder energi och det mesta av energin kommer från icke-förnyelsebara källor. Sverige har visserligen en hög andel förnyelsebar energi jämfört med andra länder men ändå är mer än hälften av energin som vi använder icke förnyelsebar. Syftet med den här rapporten är att utveckla ett mer hållbart samhälle genom att använda solenergi. Målet har varit att undersöka hur solenergi används i nybyggda villor och hur användningen av solenergi kan öka. Tre huvudfrågor har utarbetats för att kunna nå målet. Hur används solenergi idag? Hur kan användningen av solenergi öka i nyproducerade villor? Hur ser användningen av solceller ut i ett internationellt perspektiv? Dessa frågor besvaras i den här rapporten med hjälp av litteraturstudier och intervjuer. En genomgång av ett stort antal rapporter och böcker om solenergi som skrivits under de senaste fem åren har gjorts. Uppgifter ifrån småhustillverkare och leverantörer har inhämtats genom intervjuer både personliga möten och via telefon. Resultatet visar att solenergi är en hållbar lösning för framtiden men den används i liten utsträckning idag. I Sverige finns det idag 30 000 småhus som har solfångare och mindre än 900st installationer med solceller. Småhustillverkare erbjuder nästan aldrig någon form av solenergi till sina hus och menar också att efterfrågan är dålig. För att kunna öka användningen av solenergi i nyproducerade villor krävs information, statlig styrning och anpassade lösningar. Marknadsföring, nettodebitering, bidrag ifrån staten, hårdare energikrav, dyrare elpriser samt lösningar som är estetiska, driftsäkra och praktiska är också förslag som framkommer i rapporten. Internationellt pågår det en mycket stor ökning av andelen solceller. Vissa länder har uppnått att el ifrån solceller har lägre eller samma pris som konventionella källor till el. I Danmark ökade installationer av solceller från 11MW till 327MW under 2012. Under 2012 installerades det totalt 100 000 MW solceller i hela världen. / Less than one hour's sunshine on our planet contains more energy than the whole world's energy consumption in one year. A common roof for residential dwellings in Sweden receives several times more energy in one year than what its needs are. The potential for solar energy is huge. At the same time the society today uses large amounts of energy and most of the energy comes from non-renewable sources. Sweden does have a high percentage of renewable energy compared to other countries but more than half of the energy we use are non-renewable. The purpose of this report is to obtain a more sustainable society by using solar energy. The goal has been to investigate how solar energy is used in the newly built small houses and how the use of solar energy can increase. Three main issues have been developed in order to achieve the purpose. How is the use of solar energy today? How can solar energy increase in newly constructed homes? How is the use of solar cells in to an international perspective? These questions have been answered in this report using literature reviews and interviews. A review of numerous reports and books on solar energy in the last five years has been done. Data from small houses manufacturers and suppliers have been obtained by interviewing both in personal meetings and by phone. The results show that solar power is a viable solution for the future, but it is used to a small extent today. In Sweden, there are 30,000 single-family homes that have solar panels and less than 900 installations with solar cells. Small houses manufacturers offer almost never any kind of solar energy into their houses and they also says that demand is poor. In order to increase the use of solar energy in small houses, information, government control, and customized solutions are all needs. Marketing, net metering, grants from the state, tougher energy requirements, higher electricity prices, and solutions that are aesthetic, reliable, and practical are also possibilities presented in the report. Internationally, it is a very large increase in the proportion of solar cells. Some countries have reached that electricity from solar cells is lower or the same price as conventional electricity sources. In Denmark, installations of solar cells increased from 11MW to 327MW in 2012. In 2012 it was installed 100,000 MW solar cells worldwide.

Photovoltaic is a renewable energy technology that creates electricity by converting the energy of light. Photovoltaics are usually installed on buildings. In this pilot study, the viability of such an installation on the roof of the school Heby skola is examined with respect to produced electricity, economic potential and environmental impact. This is done with the software Solelekonomi, together with 11-years of solar irradiance data and measurements of the properties of the intended roof, which made it was possible to simulate the production patterns of a photovoltaic system. The simulations were made on two possible system sizes 50 m2 and 200 m2 with respectively 7.75 and 31 kWpeak installed power. Among other things, the results showed that 1.1% and 4.45% of the total electricity consumption could be replaced by the systems. A PV investment was found to be a good option with respect to the sections examined. Furthermore, considering PVinstallations, the school was found to be representative for schools in Sweden, and thus this essay can provide a basis for other PV pilot project on Swedish schools.

Increasing global energy demands and diminishing supplies of conventional fuels are forcing the world to focus more on alternative power sources that are both renewable and ecologically benign. Solar energy is clean, regularly available and can be harvested without sacrificing valuable land space. Due to the associated cost of solar cells, however a very small portion of the world’s energy needs are supplied by the sun. Solution-processable organic photovoltaics (OPVs) offer the promise of lower production costs relative to conventional (silicon) solar cell technology. Solution-processing can be performed using reel-to-reel manufacturing, with printing and coating techniques that are significantly cheaper than current processing methods for inorganic semiconductors. Although OPV efficiency values currently remain inferior to those of conventional solar cells, the rate of improvement is much higher in OPVs than in other solar cell technologies. Recently an efficiency exceeding 10% was reported for organic solar cells. An important difference between organic and conventional solar cells is the charge carrier mobility of the semiconductors, which tends to be relatively low in organic semiconductors. Recent advances in molecular design have led to polymer semiconductor materials that possess hole mobility values similar to that of amorphous silicon. The present study investigates potential improvements in OPV devices that can be achieved through the application of high hole mobility polymer semiconductor donors. Two diketopyrrolopyrrole-based polymers, PDQT and PDBFBT, were selected for the role of electron donor in OPV devices due to their high mobilities and their optimum optical and electrical properties. Optimization of the process parameters was performed using PC61BM as the acceptor. A relatively high quantity of PC61BM (3 - 4 × the weight of the donor) is required in the donor-acceptor blends of both polymers in order to balance the high hole mobility. For these donor-acceptor blends, a solvent system consisting of chloroform/ortho-dichlorobenzene (4:1 v/v) is necessary for proper solubility, and an additive, 1,8-diiodooctane, is required to achieve an acceptable morphology. The main benefit expected from the use of high mobility semiconductors is reduced charge recombination. This was studied in relation to the active layer thickness in standard and inverted OPV devices prepared using PC61BM as the acceptor. Normally the thickness of the active layer is required to be low (~100 nm) due to the poor charge transport mobility of the carriers. In this study, rather consistent power conversion efficiencies were achieved throughout a wide range of active layer thicknesses (~100 nm to ~800 nm). A comparison between standard and inverted device configurations demonstrates that the inverted configuration is more suitable for achieving thicker active layers when a high hole mobility donor is used. This is attributed to the longer hole collection path in the inverted structure, which can benefit from using a high hole mobility material. Increasing the absorption spectra of the donor-acceptor blend was studied by substituting PC71BM for PC61BM. The improved absorption leads to greater charge generation. In PDQT devices, the increase in absorption that is contributed by PC71BM appears to be of greatest benefit when active layers are not very thick. Therefore, when thick active layers (>500 nm) are required, the use of PC61BM is sufficient, in conjunction with a high mobility donor. Finally, an increase in a polymer’s crystallinity can often lead to greater mobility. This can be accomplished through various annealing techniques. The improved crystallinity of PDBFBT that occurs as a result of thermal annealing was studied in OPV applications. Although hole mobility of PDBFBT in the lateral direction improves with thermal annealing, mobility in the vertical direction decreases with increasing temperature. This suggests that the crystallinity of PDBFBT is oriented in the lateral direction as opposed to the vertical direction, thereby directing charge flow horizontal to the surface. With thermal annealing, an optimal amount of PC61BM added to PDBFBT can increase the vertical mobility to fairly high values. Nevertheless, the efficiency of standard and inverted OPV devices decreases with increased annealing temperature. This is attributed to agglomeration of PC61BM that occurs from an increase in annealing temperature. The results of this study demonstrate that thermal annealing is not beneficial for PDBFBT:PC61BM films in OPV applications due to the vertical orientation of devices. All of the studies presented in this work involve the use of high hole mobility polymer semiconductors as donor materials for OPV applications. This work will provide a deeper understanding of the properties required for the development of new semiconductor materials in OPV applications. Furthermore, this work will be very useful for the design of device structures for more feasible manufacturing of large area OPV devices via high speed roll-to-roll printing processes.

Organic solar cells have caught considerable attention in the past few years due to their potential for providing environmentally safe, flexible, lightweight, inexpensive, and roll-to-roll feasible production solar cells. However, the efficiency achieved in current organic solar cells is quite low, yet quick and successive improvements render it as a promising alternative. A hopeful approach to improve the efficiency is by exploiting the tandem concept which consists of stacking two or more organic solar cells in series. One important constituent in tandem solar cells is the middle electrode layer which is transparent and functions as a cathode for the first cell and an anode for the second cell. Most studies done so far have employed noble metals such as gold or silver as the middle electrode layer; however, they suffered from several shortcomings especially with respect to reproducibility. This thesis focuses on studying a new trend which employs an oxide material based on nano-particles as a transparent cathode (such as Zinc-oxide-nano-particles) along with a transparent anode so as to replace the middle electrode. Thus, this work presents a study on solution processable zinc oxide (ZnO) nanostructures, their proper handling techniques, and their potential as a middle electrode material in Tandem solar cells in many different configurations involving both polymer and small molecule materials. Moreover, the ZnO-np potential as a candidate for acceptor material is also investigated.

Background: The purpose of this master thesis was to investigate what generic strategies are utilized by big players in the solar photovoltaic industry to improve their competitive positions. The continuous expansion of the solar market indicated the significance of this research, since the correctly chosen strategy has a direct influence on the success and prosperity of the growing and developing high tech companies.Aim: The first aim of the study was to examine the applicability of Michael Porter‟s theory of generic strategies to the high tech industry, to be more precise the solar photovoltaic industry. The second aim of the study was to explore the cases, if any, when the simultaneous pursuit of more than one generic strategy was possible. The last but not the least aim was to deeply investigate the potential of the differentiation strategy and the effect it has on the companies.Definitions: The continuous utilization of the following concepts is present in the research: Generic strategies – the three different strategic approaches – cost leadership, differentiation, and focus – the companies can undertake to build a strong competitive advantage and outperform their competitors Differentiation – a case when a firm‟s offering is preferred, on some buying occasions (or by some customers all of the time) over rival firm‟s offerings Solar energy – alternative solutions of receiving energy directly from the sun – using solar modules which convert sunrays into electricityMethodology: Qualitative research methodology was used in this study. The in depth analyses of three case companies were done mainly by means of collecting the secondary data. In addition to that two out of three companies were contacted in order to conduct personal interviews via phone and email. Their answers were used as a supportive tool for the developed propositions.Results: The collected and analyzed secondary data together with the outcomes of the interviews revealed the flaws and limitations of Porter‟s theory. The simultaneous pursuit of two strategies was proven not only to be taking place, furthermore, to be leading to prosperity in some situations. The new model was developed which showed that the pursuit of two strategies is more of a necessity under certain circumstances. A thorough examination of the differentiation concept resulted in discovering the ways and methods which could be used by companies to strengthen their market positions.

Solar photovoltaic has become one of the potential solutions for current energy needs and for combating greenhouse gas emissions. The photovoltaics (PV) industry is booming, with a yearly growth rate well in excess of 30% over the last decade. This explosive growth has been driven by market development programs to accelerate the deployment of sustainable energy options and rapidly increasing fossil fuel prices. Currently, the PV market is based on silicon wafer solar cells (thick cells of around 150–300 μm made of crystalline silicon). This technology, classified as the first-generation of photovoltaic cells. The second generation of photovoltaic materials is based on the introduction of thin film layers of semiconductor materials. Unfortunately, the conversion efficiency of the current PV systems is low despite the lower manufacturing costs. Nevertheless, to achieve highly efficient silicon solar cell devices, the development of new high quality materials in terms of structure and electrical properties is a must to overcome the issues related to amorphous silicon (a -Si:H) degradation. Meanwhile, to remain competitive with the conventional energy sources, cost must be taken into consideration. Moreover, novel approaches combined with conventional mature silicon solar cell technology can boost the conventional efficiency and break its maximum limits. In our approach, we set to achieve efficient, stable and affordable silicon solar cell devices by focusing on the development of a new device made of epitaxial films. This new device is developed using new epitaxial growth phosphorous and/or boron doped layers at low processing temperature using plasma enhanced chemical vapor deposition (PECVD). The junction between the phosphorous or boron-doped epitaxial film of the device is formed between the film and the p or n-type crystalline silicon (c-Si) substrate, giving rise to (n epi-Si/p c-Si device or p epi-Si/n c-Si device), respectively. Different processing conditions have been fully characterized and deployed for the fabrication of different silicon solar cells architectures. The high quality epitaxial film (up to 400 nm) was used as an emitter for an efficient stable homojunction solar cell. Extensive analysis of the developed fine structure material, using high resolution transmission electron microscope (HRTEM), showed that hydrogen played a crucial role in the epitaxial growth of highly phosphorous doped silicon films. The main processing parameters that influenced the quality of the structure were; radio frequency (RF) power density, the processing chamber pressure, the substrate temperature, the gas flow rate used for deposition of silicon films, and hydrogen dilution. The best result, in terms of structure and electrical properties, was achieved at intermediate hydrogen dilution (HD) regime between 91 and 92% under optimized deposition conditions of the rest of the processing parameters. The conductivity and the carrier mobility values are good indicators of the electrical quality of the silicon (Si) film and can be used to investigate the structural quality indirectly. The electrical conductivity analyses using spreading resistance profile (SRP), through the detection of active carriers inside the developed films, are presented in details for the developed epitaxial film under the optimized processing conditions. Measurements of the active phosphorous dopant revealed that, the film has a very high active carrier concentration of an average of 5.0 x1019 cm-3 with a maximum value of 6.9 x 1019 cm-3 at the interface between substrate and the epitaxial film. The observed higher concentration of electrically active P atoms compared to the total phosphorus concentration indicates that more than half of dopants become incorporated into substitutional positions. Highly doping efficiency ηd of more than 50 % was calculated from both secondary ion mass spectroscopy (SIMS) and SRP analysis. A variety of proposed structures were fabricated and characterized on planar, textured, and under different deposition temperatures. Detailed studies of the photovoltaic properties of the fabricated devices were carried out using epitaxial silicon films. The results of these studies confirmed that the measured open circuit voltage (Voc) of the device ranged between 575 and 580 mV with good fill factor (FF) values in the range of 74-76 %. We applied the rapid thermal process (RTP) for a very short time (60 s) at moderate temperature of 750oC to enhance the photovoltaic properties of the fabricated device. The following results were achieved, the values of Voc, and the short circuit current (Isc) were 598 mV and 27.5 mA respectively, with a fill factor value of up to 76 % leading to an efficiency of 12.5 %. Efficiency enhancement by 13.06 % was achieved over the reference cell which was prepared without using RTP. Another way to increase the efficiency of the fabricated device is to reduce the reflections from its polished substrate. This was achieved by utilizing the light trapping technique that transforms the reflective polished surface into a pyramidical texturing using alkaline solutions. Further enhancements of both Voc and Isc were achieved with values of 612 mV and 31mA respectively, and a fill factor of 76 % leading to an increase in the efficiency by up to 13.8 %. A noticeable efficiency enhancement by ~20 % over the reference cell is reported for the developed devices on the textured surfaces. Moreover, the efficiency of the fabricated epitaxial silicon solar cells can be boosted by the deployment of silicon nanocrystals (Si NCs) on the top surface of the fabricated devices. In the course of this PhD research we found a way to achieve this by depositing a thin layer of Si NCs, embedded in amorphous silicon matrix, on top of the epitaxial film. Structural analysis of the deposited Si NCs was performed. It is shown from the HRTEM analysis that the developed Si NCs, are randomly distributed, have a spherical shape with a radius of approximately 2.5 nm, and are 10-20 nm apart in the amorphous silicon matrix. Based on the size of the developed Si NCs, the optical band gap was found to be in the region of 1.8-2.2 eV. Due to the incorporation of Si NCs layer a noticeable enhancement in the Isc was reported.

Since the carbon nanotubes were first discovered by Iijima in 1991, CNTs have been the focus of intense research by many groups. Nearly 7000 papers and 700 theses on carbon nanotubes can be found from the eminent journals such as Nature and Science in the last decade. Since carbon nanotubes show impressive mechanical, physical and electronic properties such as high stiffness, high strength, low density, and excellent thermal conductivity, suggesting its role in light-weight high strength material application. A great quantity of important research has evidently been done in this field. The purpose of this thesis research is to investigate the feasibility of MWCNTs for the application of polymer organic photovoltaics, and to study the formed MWCNTs-P3HT polymer nanocomposites properties, which are optical absorption, fluorescence emission, and morphology, as well as the formed photovoltaic device performance. This fundamental research would significantly contribute to the advanced technology development for how to improve the efficiency of the polymer organic photovoltaics.

A simple cost-effective approach was proposed and successfully employed to fabricate high-quality screen-printed (SP) contacts to high sheet-resistance emitters (100 ohm/sq) to improve the Si solar cell efficiency. Device modeling was used to quantify the performance enhancement possible from the high sheet-resistance emitter for various cell designs. It was found that for performance enhancement from the high sheet-resistance emitter, certain cell design criteria must be satisfied. Model calculations showed that in order to achieve any performance enhancement over the conventional ~40 ohm/sq emitter, the high sheet resistance emitter solar cell must have a reasonably good (120,000 cm/s) or low front-surface recombination velocity (FSRV). Model calculations were also performed to establish requirements for high fill factors (FFs). The results showed that the series resistance should be less than 0.8 ohm-cm^2, the shunt resistance should be greater than 1000 ohm-cm^2, and the junction leakage current should be less than 25 nA/cm^2. Analytical microscopy and surface analysis techniques were used to study the Ag-Si contact interface of different SP Ag pastes. Physical and electrical properties of SP Ag thick-film contacts were studied and correlated to understand and achieve good-quality ohmic contacts to high sheet-resistance emitters for solar cells. This information was then used to define the criteria for high-quality screen-printed contacts. The role of paste constituents and firing scheme on contact quality were investigated to tailor the high-quality screen-printed contact interface structure that results in high performance solar cells. Results indicated that small particle size, high glass transition temperature, rapid firing and less aggressive glass frit help in producing high-quality contacts. Based on these results high-quality SP contacts with high FFs0.78 on high sheet-resistance emitters were achieved for the first time using a simple single-step firing process. This technology was applied to different substrates (monocrystalline and multicrystalline) and surfaces (textured and planar). Cell efficiencies of ~16.2% on low-cost EFG ribbon substrates were achieved on high sheet-resistance emitters with SP contacts. A record high-efficiency SP solar cell of 19% with textured high sheet-resistance emitter was also fabricated and modeled.