The first amorphous silicon solar cell using a p-i-n structure was developed in 1976 by Carlson and Wronski. In the following decades techniques such as hydrogenation and light trapping texturing were used to raise the efficiency of a-Si thin film solar cell from 2.4% to 9.3%. The research focus has since then shifted from single junction to multi junction solar cells. In a single junction solar cell much of the solar spectrum is underutilised. As photon energy that exceeds the bandgap is wasted as heat, and photons with energy below the bandgap can not be absorbed. In a multi junction structure this problem can be solved by tailoring each layer of the solar cell to a specific range of the solar spectrum, thereby increasing the efficiency.

The focus of this project is to study the potential of germanium tin alloy as a low bandgap material for the bottom layer of a multi junction solar cell. This is done by depositing the a-GeSn:H layers through plasma enhanced chemical vapour deposition(PECVD) with germane and tetramethyltin(TMT) as precursor gas, and examining the optical and electrical properties of the samples made under various deposition conditions. This project will also study the effect of carbon inclusion in germanium, due to it being a side effect of using TMT as a precursor gas.

This study analyzed the profitability and cost constraints of thin film solar PV modules for commercial sized lightweight roofs by using the reversed LCOE method. The focus will be on a particular technology of solar PV, namely, thin film solar PV module technology. Thin film solar PV modules are able to serve the niche market of commercial scale lightweight roofs, without competition with the highly matured traditional solar PV market. As such, the objective of this study is to derive actionable insights into the cost constraints of thin-film solar PV modules for these applications. Using the reversed LCOE method, figures show that there is a high variability in conditions that influences the performance and the profitability of thin film solar PV modules in a commercial scale lightweight roof project. This study shows that both profitable and unprofitable scenarios are possible and provides an analysis on how various conditions influence the project’s profitability.

This thesis aimed to process and characterize hydrogenated germanium (Ge:H) films to use them as a low-bandgap intrinsic absorber layer. The bandgap of Germanium can go down to 0.67 eV. A p-i-n solar cell consisting of intrinsic germanium film produced using Plasma Enhanced Chemical Vapour Deposition (PECVD) can be inexpensively paired with crystalline silicon and other semiconductor materials to produce a multi-junction solar cell with high efficiencies. Such a cell would utilize the lower part of the solar spectrum currently untapped in commercially available mass-produced solar modules. Previous research had deposited Ge:H films using a counterflow PECVD reactor, as compared to a showerhead configuration in the reactor used in this research.

The study consisted of experiments that explored the properties of the germanium film deposited. First, the deposition parameters of PECVD were varied to study its effect on important film properties. Since the germanium layer will be used in a solar cell as the absorber layer, the band-gap and activation energy were the most critical parameters to monitor film intrinsicity. Experiments were performed by depositing germanium layers on glass substrates and silicon wafers to understand the properties of the films when deposited at different temperatures and also when the germane flow was altered. The effect of the power and pressure on the properties of the germanium samples was studied too. In all these experiments, the deposition time and electrode gap are kept constant. The processing window of 3-4.5 mbar and 12-20 W where intrinsic amorphous germanium (a-Ge:H) films can be produced was identified.

Single junction solar cells in p-i-n and n-i-p configuration were then incorporated with the intrinsic amorphous germanium. The p-i-n configuration displayed solar cell characteristics, whereas the n-i-p configuration cells did not, despite the changes in doping of the p-layer. Further experiments were carried out to look into the stability of the material by repeating the J-V curve measurement of the first cell that showed solar cell characteristics, but similar behaviour was not observed. Additionally, Raman spectroscopy was carried out, which revealed that the material is amorphous.

In summary, the results look promising in proving these films as a suitable material for an intrinsic absorber layer. It also strongly suggests that the showerhead PECVD configuration can lead to better control of reaction mechanics, giving films with desired material properties. The layer can be used as an intrinsic layer in a p-i-n structure device, but further investigation is required to look into the interaction of the layers of the solar cells.

This study presents a comprehensive Life Cycle Assessment (LCA) comparing HyET Solar's Powerfoil modules to conventional Passivated Emitter Rear Contact (PERC) technology. Through both current and future scenario analyses, utilizing tools like Integrated Assessment Models (IAMs) and Shared Socioeconomic Pathways (SSPs), the research examines key impact categories, including Global Warming Potential (GWP), Terrestrial Acidification, Land Use, and Material Resources.
Current scenario findings reveal that PERC modules exhibit significantly higher environmental impacts across most categories. The GWP of PERC modules is notably high at 50.1 grams CO2-equivalent per kWh, primarily driven by energy-intensive processes in inverter and silicon wafer production. Powerfoil modules, especially the triple-junction architecture, demonstrate reduced impacts with emissions as low as 23.8 grams CO2-equivalent per kWh.
Future scenario findings project even greater environmental benefits for Powerfoil modules by 2050. Efficiency improvements and material optimizations, including the replacement of existing top encapsulant and reducing the carrier foil thickness, could bring down the emissions to 6.2 grams CO2-equivalent per kWh, which is almost 70% lower than PERC modules.
The study also identifies critical hotspots in the Powerfoil modules’ lifecycle, providing a quantitative analysis of environmental impacts after replacing these hotspots in future scenarios. Furthermore, the Global Sensitivity Analysis highlights that module efficiency and solar irradiation are critical factors influencing environmental outcomes. These findings highlight the potential of Powerfoil modules as a more sustainable alternative in photovoltaic technology, with substantial implications for reducing the environmental footprint of energy systems.

This thesis investigates the formation of hotspots in single junction amorphous silicon thin film solar modules through experimental methods. Employing electroluminescence (EL) imaging and infrared (IR) imaging, the study aims at identifying and classifying defects that can be used to predict hotspot formation and assesses the endurance of different sized modules.
To predict hotspot formation on small 30 by 30 cm monolithically interconnected modules, the research first categorises shunts into four different classes based on their severity and localization (Mode A, Mode AB, Mode B and Mode C). Mode A defects are severe and cover a large area, Mode B defects are severe and localized, Mode AB defects are severe and rather localized and Mode C defects are weak and localized. It was found that only shunts that are severe and localized lead to the formation of hotspots (Mode B and rather localized Mode AB). Since no hotspots formed at locations without predictors EL based shunt classification has proven to be an effective predictor with high predictive accuracy for hotspots.
Industrial modules with a dimension of 190cm by 30 cm exhibit similar defect behavior, however the interaction between multiple hotspots within one cell leads to some exceptions. When multiple defects are located within the same cell, the most severe and localized defect forms a strong hotspot, while the other defects either form weaker hotspots or no hotspots at all. Due to a higher current level also Mode C defects can lead to hotspot formation when they are the most severe defect within a cell. Furthermore locations that show defect cluster or current crowding also experience strong hotspot formation. Lastly, shunts that were found to be originating from scribe defects are prone to form strong hotspots.
EL based shunt classification has therefore proven to be a reliable predictor for hotspot formation on modules of different sizes. Furthermore this procedure did not induce any performance losses on the modules. However the EL imaging procedure itself is quite time intensive and therefore not suitable as a quality test that could be implemented at the end of a production line.
Using IR imaging in reverse bias, hotspots can reliably be identified on small and large modules. Due to higher current levels, hotspots can easier be identified on large modules. However high reverse currents can lead to significant damage and loss of performance of the modules. IR imaging in reverse has proven to be a faster alternative for hotspot detection, suitable for production line integration.
The findings contribute to improved defect identification and hotspot prediction techniques, enhancing the reliability of solar module manufacturing and maintenance processes. Future work should focus on refining defect classification and exploring the behaviour of hotspot formation and impacts on reliability in field applications.

The characteristic feature of ”thin” film solar cells is that they are thin, ranging over thicknesses of a few micrometers. This results in a drop in the light trapping capability of the solar cell, owing to the Beer-Lambert law. Thus, there is a need to optimize light management to enhance the amount of light being trapped in the photoactive region. This can be done by imparting texture in the glass superstrate to scatter the light and thereby allowing the light to travel over a longer distance in the absorber.

In this thesis, the focus is mainly on developing a high-quality reproducable procedure for achieving periodic texturing in glass and understanding the enhancement in the optical impact of the surface. the first objective was to understand the influence of the different processes involved in the fabrication procedure of periodic textured glass superstrates. This was done by varying the parameters associated with the individual processes and observing the resultant impact on the deterministic characteristics of the texturing process. The influence of the mask design, employed in the photolithography process, on the dimensionality of the texture was also analyzed. Based on the aforementioned results, an optimized recipe was developed and successfully implemented to enhance the depth of the periodic hexagonal texturing imparted onto the glass. Additionally, an indicative parameter Re/P was developed to imply the effect the processes had on the quality of the texturing.

This project also ventured into studying the growth of nanocrystalline silicon on the deep textures developed using the optimized recipe. Following this, an extensive optical analysis of the honeycomb textured superstrates was carried out to realize the scattering effect induced by this texturing on interacting with light. This was done by studying the transmittance components and the angular intensity distribution of the periodic textured glass. The interaction mechanism of the textures was found to be dependent on the wavelength and
the size of the textures. In general, there was a linear increase in the diffuse transmittance with texture height, for all wavelengths of light. However, it was noticed that the slope of this relationship varied for the different wavelengths, since it was mainly dominated by different scattering mechanisms for different wavelengths. Finally, the influence of the optical impact of these hexagonal textures on solar cell performance was also studied by studying the Jsc of the micromorph tandem solar cells, developed on deep hexagonal textures of different periodicities.

The global shift towards low-carbon and renewable energy sources, driven by climate concerns associated with fossil fuels, has positioned solar photovoltaics (PV) as a major alternative. With the increasing adoption of PV technologies, it is crucial to study various PV module types. This thesis focuses on the HyET Powerfoil, an amorphous silicon (a-Si) PV module with a polymer encapsulation, offering a lightweight alternative to conventional crystalline silicon (c-Si) PV modules. Due to the new type of polymer encapsulation (TE) and to compare a-Si absorber with its c-Si counterparts, numerous factors must be examined before large-scale outdoor deployment to prevent failure and degradation and assess module reliability.

This research addresses the losses observed in HyET Powerfoil modules, leading to the design of an experiment involving two groups of four modules each to identify and segregate potential degradation at the interfaces. The modules included 2 c-Si glass-encapsulated PV modules, 2 c-Si glass + TE encapsulated modules, 2 HyET modules with glass encapsulation, and 2 HyET Powerfoils. The primary objective was to investigate factors contributing to performance losses especially the short-circuit current (Isc) and soiling compared to traditional glass-encapsulated modules. The study utilized measurements from a monitoring system and a solar simulator, along with regular cleaning. Initial findings indicated significant absorber degradation, with HyET Powerfoils showing a degradation rate of around 17% at the final measurements. Additionally, the TE polymer exhibited substantial losses in transmission due to degradation and soiling.

The thesis also addresses optical degradation in HyET Powerfoil modules, particularly focusing on the TE polymer stack. Using a combination of outdoor exposure tests, WOM ageing, and surface roughness measurements, the study assessed degradation mechanisms. The results indicate that the TE polymer stack experiences significantly higher soiling of around 1% more than glass. This can be attributed to increased surface roughness. Moreover, the adhesive used in the TE polymer stack was identified as a major contributor to optical degradation, leading to increased light scattering of around 5%. These findings suggest that while TE polymers offer certain benefits, their long-term durability under various environmental conditions needs further optimization.

Additionally, an injection-dependent Electroluminescence (EL) predictor was developed to screen for hotspots, based on the IEC 61215 Hotspot Endurance Tests. Defects visible in the EL images were classified into three modes based on defect intensities: Mode A, Mode B, and Mode C. Further testing revealed that only Mode B defects led to hotspot formation due to their localized effects.

In conclusion, while the flexible HyET Powerfoil demonstrates the potential to facilitate high-efficiency modules for lightweight applications, specific areas in the polymer configuration need improvement. This study indicates potential pathways for enhancing the long-term performance of these modules.

Renewable energy sources, such as thin-film silicon solar cells, show a lot of potential as the technology promises low production temperatures, low cost and low material usage. Other benefits are the flexible and very lightweight modules that can be fabricated, which enable a wide variety of applications. Other benefits include the low-temperature coefficient and low toxicity of the materials used to create thin-film silicon solar cells. The downside of using thin-film silicon modules is the relatively low power conversion efficiency inherent to the amorphous and nanocrystalline silicon. Another downside of amorphous silicon solar cells is their significant initial degradation, known as the Staebler-Wronski effect. This initial degradation will stabilize after time but does limit the ultimate conversion efficiency, especially for single-junction devices.
Hydrogenated amorphous silicon (a-Si:H) and nano-crystalline silicon (nc-Si:H) solar cells can be added in series to form a tandem device, thus increasing the efficiency of thin-film silicon solar cells. Although the current will be limited for 2-terminal tandem devices, a significant increase in open circuit voltage can be achieved resulting in higher efficiencies. To achieve highly efficient thin-film silicon solar cells a combination of good optical, electrical and material properties need to be combined. Extensive research has been done to achieve such high-efficiency devices focussed on the silicon deposition conditions, glass texturing for effective light scattering and light incoupling through anti-reflection coatings. Further research is focused on Transparent Conductive Oxides (TCO) improvements and the creation of triple or quadruple junctions.
Firstly, this thesis will focus on a literature study on amorphous silicon with a high-energy bandgap, deposition conditions in PECVD chambers and an i-SiOx buffer layer. A top cell of amorphous silicon with a high-energy bandgap can improve the conversion efficiency of a-Si:H/nc-Si:H solar cells by increasing its overall V oc. The amorphous silicon is processed at high pressure (3-9mbar) and high power densities (150-400mW /cm2) in a VHF-PECVD chamber at 40.68M Hz. To improve the poor blue response of these solar cells, a buffer layer of i-SiOx is explored as such a buffer layer has proven itself under normal deposition power densities (28mW /cm2) and pressure (0.7mbar).The i-SiOx did not prove to be effective in improving the blue response. A narrow range of deposition conditions around 5mbar and 25W is found to give high-bandgap energy solar cells with a good blue response.
Secondly, literature findings on a bilayer TCO configuration of IOH (Hydrogenated Indium Oxide) and i-ZnO (intrinsic Zinc-Oxide) to improve nc-Si:H single junction solar cells are provided. Prior studies on the use of a back reflector made out of different ZnO(Zinc-Oxides) are presented. Findings in literature on micro and nano-textured glass are presented and a comparison is made in an experiment to justify the use of a specific texture. Further experiments are carried out to measure the effect of implementing the bilayer TCO and an i-ZnO back reflector and an experiment on the performance and reproducibility of a-Si on MST (modulated surface textured) glass substrates is performed. ITO textured glass is chosen as the best performing substrate and a thick 1μ i-ZnO layer as part of a bilayer TCO is shown to be most effective at light scattering. The i-ZnO as part of a bilayer TCO can also significantly improve the spectral response of a-Si:H solar cell on MST textured glass. Furthermore, the i-ZnO as a back reflector is shown to be more effective when its thickness is increased.
Thirdly, a study is performed on the functioning of the a-Si:H/nc-Si:H tandem cells with respect to the thickness of the p-layer in the tunnel recombination junction (TRJ). An experiment is carried out to improve the reproducibility of a-Si:H/nc-Si:H solar cells by increasing the hickness of p-layer in the TRJ.
The conclusion is made that the glass texturing is more influential than the thickness of the p-layer in this experiment. Further investigation of the p-layer at the front interface of the device is done by an experiment on both MST and Asahi substrates. It is shown that thicker front players do not improve the reproducibility of tandem solar cells, but a trend of more parasitic absorption is seen. Finally, a study on micro and nano-textured glass for a-Si:H/nc-Si:H solar cells is shown. The chosen ITO substrate is finally chosen to demonstrate the progress of ongoing research on the performance of a-Si:H/nc-Si:H solar cells. The bilayer TCO vs a single layer TCO is used in combination with and without a SiNx ARC.
The electrical performance of the solar cells deposited in the final experiment is likely limited by poor IOH depositions and a large contribution of parasitic absorption is shown for the samples with the SiNx ARC. Either interaction of SiNx with the IOH or a poor IOH deposition are the most likely causes. Good 1-R curves are obtained for the solar cells on ITO textured glass substrates, especially the sample with the bilayer TCO and SiNx ARC.

Thin film solar cells are devices that make use of thin layers to generate electricity from solar energy. Among various layers present in a thin film solar cell architecture, transparent conductive oxide (TCO) is crucial. TCOs are a set of materials with a unique set of properties. As a front contact, TCOs are required to offer high transparency to allow photons to reach the absorber layer to generate charge carriers. At the same time, TCOs need to be conductive as well to transport charge carriers from absorber to the metal electrode. However, there exists a trade-off where improvement to one property often comprises the other.
The concept of a bi-layer TCO configuration is explored in this project which makes use of two single layer TCOs: one with superior electrical properties and the other with superior optical properties. Hydrogenated indium oxide (IOH) is investigated as the conductive layer while the intrinsic zinc oxide (i-ZnO) as the transparent layer. Various other conductive layers are also tried in combination with i-ZnO, those being - Cerium doped indium oxide (ICO) and Cerium and hydrogen co-doped indium oxide (ICOH).
The first step to produce highly conductive bi-layer films is optimise post-deposition annealing parameters. Emphasis is placed on optimising annealing time, which tracing out the behavior of change in opto-electrical properties of the bi-layer after every 10 min increment in annealing time. 140 minutes is found as the optimum annealing time for IOH/i-ZnO bi-layers on both flat glass and textured glass substrates.
Novel highly conductive IOH/i-ZnO bi-layer were deposited demonstrating mobility of 143 𝑐𝑚^2/𝑉 𝑠 and carrier concentration of 1.05𝑥10^19 𝑐𝑚^−3 on flat glass. The bi-layer has the ability to not only retain individual constituent TCO properties and also to surpass the limitations of their individual TCOs. This attributes to the fact that the free charge carriers transport takes place a t the interface between TCO layer in the bi-layer stack. The ICO/i-ZnO and ICOH/i-ZnO structures were deposited, both bi-layers demonstrated mobility below 100 𝑐𝑚^2/𝑉 𝑠, however they outperformed their layers both electrically and optically.
IOH/i-ZnO bi-layer construction was also deposited on textured glass substrates. Best sample demonstrates mobility as high as 110 𝑐𝑚^2/𝑉 𝑠 with a carrier concentration of 3.63𝑥10^19 𝑐𝑚^−3. The reason for slightly lower mobilities is attributed to the inconsistency in shape and size of the textures present on the substrate, which leads to non-uniform deposition of IOH across the entire surface. Further investigation will lead to understanding hydrogen’s role in the IOH/i-ZnO bi-layer and the extent to which bi-layer performance on textured substrates can be improved.

Thin-film amorphous Silicon (a-Si) technology has been up and coming in recent years in order to achieve an efficiency comparable to crystalline Silicon (c-Si). Although the technology has existed for quite some time, it has not been researched as much as its crystalline counterpart, especially not in the hotspot reliability sector. The hotspot phenomenon is noticed in field-aged modules commonly due to partial shading or soiling losses. When one of the cells in a string gets partially or fully shaded, the shaded cells are forced to be in reverse bias and dissipate power in the form of heat, causing the formation of hotspots. The hotspots can reach temperatures of beyond 100C. These can lead to the melting of module encapsulants and faster degradation of the module, as well as being a fire hazard because of the elevated temperatures. This thesis was done in collaboration with HyET Solar BV, a company that produces a-Si thin film solar foils. The modules used in this thesis are from HyET Solar BV and we have selected highly degraded modules for the experiments.

This report aims to achieve a couple of things: first, get insight of hotspot formation in a-Si thin-film modules in accordance with the latest International Electrotechnical Comission (IEC) 61215 Certification norms.

Secondly, we have utilized electroluminescence (EL) imaging to classify various defects present in the modules and to evaluate their endurance to hotspot formation. Based on those results, we created a map that shows the probability of hotspot formation from different defects in the degraded modules.

And lastly, we classified the different kinds of hotspots based on factors like shape and location. Also, the possibilities of how these defects originated are explained on the basis of a schematic overview of the interconnection between the cells.

After testing and experimenting, it became apparent that the highly degraded a-Si foils are susceptible to hotspot formation. After light soaking two foils according to the IEC 61215 norms, a couple of hotspots were created in the shaded area. Some of these hotspots could be seen on EL images by defects before they became visible during the visual inspection step. EL imaging is used to characterize different defects that could lead to hotspot formation. These defects are white dots, current crowding and dark regions. The probability map for these defects is as follows: 46.6% of the white dots have turned into hotspots, 16.7% for current crowding and 32% for dark regions. It is suspected that these white dots are a manufacturing process problem; they could be areas of high-impurity contaminants or a sharp point. Current crowding and dark regions are always paired together and depending on which side of the cell they are on, it is suspected that it is a fault in either the P2 or P3 scribes of a cell in the module.

Thin-film silicon solar cells are an innovative approach to utilizing solar energy. Thanks to their flexibility, lower material usage, and production cost, they have the potential to be used in a range of applications. The conversion efficiencies of thin-film silicon solar cells need to be improved to make them commercially viable. This involves further optimizing the different layers of the solar cells. During this project, different strategies for enhancing thin film silicon solar cells were studied, including the deposition conditions for nc-Si:H layer, the sacrificial texturing used, the use of an additional back reflector layer, and the type of TCO layer used. A more consistent quality of the nc-Si:H samples were obtained by varying the hydrogen flow rate compared to the silane flow rate in the processing chamber. Using a silane flow rate of 2.3 sccm and a hydrogen flow rate of 120 sccm, a silane concentration 2.6 was achieved, resulting in nc-Si:H layer with a crystallinity of 60%, close to the desired amorphous-nanocrystalline silicon transition region. The texturing used in the glass sample can play a significant role in scattering the incident light into the solar cell. Craters of different sizes are formed depending on the material used for the sacrificial layer. Making smaller craters on top of larger craters using modulated surface textures (MST) is also possible. Using intrinsic Zinc Oxide (i-ZnO) sacrificial texturing resulted in the highest spectral utilization in single junction nc-Si: H with a Jsc of 25.2 mA/cm2. Indium-doped tin oxide (ITO) sacrificial texturing created micro-sized textures, resulting in the highest spectral utilization in micromorph samples (Jsc of 24.6 mA/cm2). Using an MST of ITO and i-ZnO also resulted in high spectral utilization with a Jsc of 24.3 mA/cm2 in micromorph cells Having an additional back reflector on top of the metal back contact can further improve photon absorption in solar cells. Using a material with a low refractive index, such as i-ZnO, increased the spectral utilization and improved the short-circuit current (Jsc) by approximately 10%. Depositing the i-ZnO back reflector layer using a higher heater temperature (300°C), improved the spectral utilization of the sample further by 9% The transparent conductive oxide (TCO) layer must be highly transparent and conductive. Usually, ITO is used as a TCO layer, although it has limited absorption in the infrared region and lower conductivity at higher temperatures. A TCO with higher optoelectrical properties was obtained using a bilayer of hydrogenated indium oxide (IOH) and i-ZnO. nc-Si:H samples with the TCO bilayer showed a higher spectral utilization and an improvement in their Jsc by 9-12%. The performance of micromorph samples with TCO bilayer was also higher with Jsc improvement of 6%. The influence of the bilayer thickness on the performance of micromorph samples was also inspected, and it was found that using a thicker bilayer with a thickness of 1100 nm instated of 600nm boosted the performance of the sample further and improved its Jsc by 3%.

Thin-film silicon photovoltaic (PV) technology has an enormous potential in the solar power market due to its light weight, flexibility and ease of integration. This enables it to have a wide range of applications like roof top and building integrated installations making it more sustainable. Some of the other key benefits of thin-film silicon PV technology include energy efficient production, less material usage, low temperature coefficient and low manufacturing cost. The relatively low conversion efficiency, however, is the major drawback of thin film silicon solar cells. Hydrogenated amorphous silicon (a-Si:H) grown by plasma-enhanced chemical vapor deposition (PECVD) is one of the extensively employed light absorbers in thin-film silicon solar cells. However, light-induced degradation (LID) of a-Si:H is one of the biggest limiting factors of this technology. LID is a metastable defect creation phenomenon that decreases the conversion efficiency of the a-Si:H solar cell after prolonged exposure to light. This is known as the Staebler-Wronski effect (SWE). SWE has been a subject of research over the past 4 decades. Despite tremendous efforts, the complete suppression of the LID has not been demonstrated yet. Nevertheless, there has been a great progress in characterisation of the defect creation and also the optimisation of solar cells to minimise the effect of LID.
In this thesis, LID of three single junction a-Si:H thin film solar cells with different qualities of a-Si:H absorber layer namely high bandgap a-Si:H, low bandgap a-Si:H and high/low bandgap a-Si:H are studied. Light soaking experiments were carried out for several hundred hours and the performance of the solar cells was analysed through external quantum efficiency (EQE) and illuminated JV characterisations at regular time intervals. Some of the key findings of the experiments include severe LID of high bandgap a-Si:H absorber layer due to increased defect creation, enhanced recombination at the p/i interface in all of the devices and also a significant relationship between the performance and light soaking temperature. Furthermore, the thermal annealing study revealed that, maximum recovery of the performance parameters can be observed at an annealing temperature of 180 ^◦C.
Based on the findings of the above mentioned study, additional experiments were carried out to investigate the stability of the devices with different materials as a buffer layer at the p/i interface. The results of the experiments revealed the significance of the buffer layer in the performance of the devices and also its influence on the LID. In addition, the analysis suggests that intrinsic silicon oxide (i-SiO_X), intrinsic hydrogenated amorphous silicon (i-a-Si:H), and p-doped hydrogenated amorphous silicon (p-aSi:H) are some of the potential candidates for a buffer layer in an a-Si:H solar cell that could give an improved stabilised performance. Furthermore, the speculation of light induced boron diffusion into
the a-Si:H bulk through the buffer layer was tested by another light soaking study to investigate effects of window layer (p) doping on LID. The study found no correlation between the window layer doping and the p/i interface degradation indicating the possibility of a different defect creation mechanism responsible for the enhanced recombination at the p/i interface.

Thin film silicon solar cells are a type of photovoltaic technology with the advantage of having thin layers of silicon to generate electricity. Unlike traditional crystalline silicon solar cells, which use thick silicon wafers, thin-film silicon solar cells use amorphous silicon that can be made with much thinner layers of silicon. This allows them to be more lightweight, flexible, and potentially less expensive to manufacture. However, their efficiency has traditionally been lower than crystalline silicon solar cells, which are more
commonly used in large-scale installations. This is primarily due to the material property of amorphous silicon, which is laden with defects and voids. Nonetheless, ongoing research and development aim to improve the efficiency and commercial viability of thin-film silicon solar cells.

HyET Solar B.V. is a company based in the Netherlands which employs a Roll to Roll (R2R) technology to produce such flexible solar cells. A temporary aluminum foil is used as the substrate on which the solar cell stack is deposited. The temporary foil is etched away, and the layers are encapsulated in low-cost polymer foils. This thesis is part of the ongoing FlamingoPV (Flexible Lightweight Advanced Materials In Next Generation of PV) project in collaboration between HyET Solar and TU Delft, to develop single, tandem, and triple junction cells with 12, 13, and 14% efficiencies, and a lifetime longer than 35 years. Part of the ongoing research to improve the performance of thin-film silicon solar cells is to understand the difference between the thin films deposited on a rigid glass substrate and flexible aluminum substrate and to investigate why the performance is lower on the aluminum substrate. In
particular, special emphasis is given to the origin of shunts in thin-film silicon solar cells, and conducting a top-down root cause analysis to investigate the origin of these shunts. Mitigation strategies are suggested to improve the solar cells fabricated on foil. Apart from this, the solar cell layers are optimized for improved electrical and optical performance on the glass substrate, to ultimately implement it on the aluminum substrate.

The key takeaways from this research are that aluminum foil was found to be a major culprit for the origin of the shunts. The foil consists of alloying elements of iron and copper, which get exposed to the surface when the foil is cleaned. When the subsequent layers are grown on the foil, the alloying elements were observed to short-circuit the device, thus causing leakage currents. Another major culprit was the formation and accumulation of silicon dust on the samples during the PECVD deposition, which was more prevalent on devices fabricated on aluminum foil. The key takeaways from the optimization experiments are that by the band-gap profiling of i-layer at a lower thickness (230nm) than the standard (300nm), we could maintain the initial electrical and optical properties of the devices. This gives us room to reduce material usage and costs at the same output performance. A permanent degradation was observed in the metal contacts of these devices, apart from the temporary light-induced degradation commonly seen in a-Si:H based solar cells. The tests conducted to improve the electrical performance did give the desired results, with an increase in the efficiency of the devices. The tests conducted to improve the optical performance did not give the desired results, with a decrease in the electrical performance and no significant increase in the optical response of the devices.

Low-cost multijunction photovoltaic devices are the next step in the solar energy revolution. Adding a bottom junction with a low bandgap energy material through plasma-enhanced chemical vapour deposition (PECVD) processing could provide a low-cost boost in conversion efficiency. A logical candidate for this low-bandgap material is germanium. A showerhead configuration instead of a direct PECVD reactor is investigated to better control reaction mechanics. In this work, hydrogenated amorphous germanium (a-Ge:H) films processed with a wide range of deposition pressures, powers, temperatures and GeH4 dilution in hydrogen are characterized using elemental analysis, vibrational analysis and analysis of the optoelectrical properties. We have identified a small processing window in which intrinsic a-Ge:H films are processed reproducibly. Two types of degradation were also studied: light-induced and oxidation in air. The lowest E04 achieved for intrinsic films was 0.8 eV with an activation energy of 0.39 eV which lies at the centre of the bandgap. The degradation experiments showed no sign of oxygen signature from EDX measurements performed after two months and FTIR measurements performed after two weeks. Light-induced degradation (LID) was performed by exposing the samples to over 80 hours; photoconductivity did not degrade below the initial value for the duration of the exposure. We believe that the showerhead configuration has increased the surface mobility of Ge-radicals during deposition, allowing them to reach sites in the layer that would otherwise be void.

This report emphasizes the importance of implementing quality control methods in the production machines at HyET Solar for assessing the quality of deposited materials. The focus is on two key steps: the deposition of the front transparent conductive oxide (TCO) layer and the deposition of silicon layers. Models were developed to characterize the quality of the TCO layer, including layer thickness, carrier concentration, and mobility of the electrons. A Drude model-based approach was chosen for in-line implementation. The sheet resistance of the TCO layer was measured using an improved tool, by enhancing its robustness and accuracy. To assess the quality of the deposited silicon layers, a non-contacting capacitive device was developed and calibrated (to measure the spatial gap between the photovoltaic layer and the device). Results showed that the Drude model fitting provided sensible results for carrier concentration and mobility with the former having a better correlation than the latter, with the standard Hall effect measurements. The results from the optical thickness model showed overestimation of values as compared to the scanning electron microscopy (SEM) results. The electrical sheet resistance values correlated well with Hall effect measurements than the optically obtained sheet resistance values. The calibrated non-contacting capacitive device demonstrated its ability to measure opto-electrical properties of the silicon layers, accurately. This research contributes to enhancing the efficiency and reliability of roll-to-roll production process of thin-film solar modules.

Thin-film silicon technology creates electricity out of micrometer thick silicon absorber layers, which makes this technology less material heavy compared to classic crystalline technology. This advantage can be further exploited with the transition towards flexible thin-film technology, where the non-modular cost can be further reduced compared to traditional crystalline solar parks ect. However, thin films have limited absorption coefficients at higher wavelengths which means the optical pathlength must be maximised to overcome this limitation. In literature, the highest efficiencies are obtained with the creation of periodic textures resulting in 10.2%, 12.7% or 14% for nanocrystalline, micromorph and triple junction silicon technology. All these cells are made on silicon substrates which means the back of the cell is textured but if the front side of the solar cell is textured, efficiencies can outperform the current holding records. A methodology is designed to create periodic micro-textures on Corning glass to improve the total absorption of lower energetic wavelengths. However, the creation of random micro-textures (Aluminum Zinc oxideand Indium Tin Oxide sacrificial texturing)(AZO-/ ITO textures) is also researched because different methodologies exist and limited knowledge exists on which methodology results in the highest amount of scattering. Second, a comparison between random and periodic textures must be made. Both types of textures undergo optical- and physical parametrisation after which both aspects are correlated to each other to gain a deeper understanding of light management. For random textures, Haze-values between 93-86% are obtained. These high values are obtained because the created craters are characterised by an increased depth for identical crater widths. Second, each methodology has its characteristic depth-width ratio which explains the optical superiority of one (ITO textures). For periodic textures, Haze-values lie between 50-3% with a maximum obtained aspect ratio of 0.18 but the optical response is not comparable to random textures because diffraction is the dominant light management technique. Therefore Angular Intensity Distribution measurements must be performed, which resulted in the conclusion that the created ITO textures stay superior (also compared to literature) while the AZO textures have a similar performance compared to the periodic texture. This translates itself in a superior external quantum efficiency (EQE) of ITO from 800nm on. Between 600-800nm, the periodic textures are superior.

The atmospheric pressure chemical vapor deposition (APCVD) process for the deposition on FTO is considered one of the most complex processes in the HyET Solar production process. An increase in the deposition speed can increase the roll-to-roll foil speed which can directly translate to lowering production costs, furthermore increasing throughput. In this thesis several experiments were performed aimed at improving opto-electrical performance while moving to higher deposition speed. However using a production machine for the experiments leads to material consumption. Henceforth, a lab-scale research tool was designed for material deposition. Thereby, optimizing the recipe and investigating the corresponding material growth can be done faster and this has been demonstrated using the lab-scale deposition tool. This tool also facilitates the investigation in different stages of growth to have a deeper understanding of each process parameter, thus making it possible to formulate the correct parameters and facilitate the knowledge transfer to the production APCVD machine.

To make silicon thin film solar cells attractive to the market, their efficiencies should reach the efficiencies of the dominant crystalline silicon solar cell. Therefore the search for ways to improve the efficiency of silicon thin film solar cells continues. TCO front contact layers and back reflector layers play a significant role in the increase of thin film solar cell efficiencies. For the optical characterization of these TCO layers, commonly used methods are found to differ significantly in results regarding the extinction coefficient which makes their accuracy questionable.

This research consists of two main parts. For the first part, the commonly used optical characterization methods spectroscopic ellipsometry and spectrophotometry + data analysis in SCOUT are analyzed in accuracy and compared to newly introduced methods using spectrophotometry + data analysis in GenPro4 and photothermal deflection spectroscopy + data analysis in GenPro4 to build a guide on optical characterization of TCO materials. For the second part, the optical response determined using the software GenPro4 of a double junction silicon thin film solar cell for a novel bi-layer front contact design consisting of IOH and i-ZnO will be compared to the optical response for standard used AZO, and ITO single layers to find the best front contact design. Furthermore, the optical response of a double junction silicon thin film solar cell for a back reflector containing an i-ZnO layer on top of the silver back contact will be compared to the optical response for a back reflector containing an AZO layer on top of the silver back contact to find the best back reflector design.

From the results of the optical characterization methods, it is concluded that photothermal deflection spectroscopy + data analysis in GenPro4 is the most accurate method for determining the extinction coefficient of a TCO material. The results of the optical simulations for front contact TCO and back reflector TCO designs showed that the bi-layer can enhance the optical response of a double junction silicon thin film solar cell significantly compared to the AZO and ITO single layers. The i-ZnO TCO back reflector layer was found to induce less parasitic absorption and therefore a better optical response of the double junction silicon thin film solar cell.

The journey towards increasing thin film solar cell efficiency is a continuously ongoing one, where each layer in the cell adds its own contributions and limitations. The transparent conductive oxide (TCO) is the first layer to encounter incident light on these cells and therefore needs to fulfil the requirement of high transparency. Carriers generated in the absorber layers of a thin film solar cell are transported to a metal electrode through the TCO, laying a conductivity requirement as well. A trade-off exists between transparency and conductivity, where one cannot be enhanced without sacrificing the other.
Indium tin oxide (ITO) currently delivers the best trade off, thus is the most commonly applied TCO.

In this thesis study, candidate TCO materials were deposited and analysed in order to surpass the opto-electrical properties of ITO. In addition to depositing ITO, hydrogen doped indium oxide (IOH) and intrinsic zinc oxide (i-ZnO) thin films were deposited using RF magnetron sputtering. Substrate temperature, RF power, deposition time and H2O partial pressure (only for IOH) were the varied parameters during depositions. IOH was found to surpass ITO in terms of conductivity, while i-ZnO surpassed ITO in terms of transparency. The best performing IOH and i-ZnO samples with regard to their respective superior parameters were chosen to be combined.

A TCO bi-layer was constructed by stacking a i-ZnO layer on top of a IOH layer. The IOH layer ensures good lateral conductivity, while the i-ZnO layer secures minimized parasitic absorption in the near infrared region. After being subjected to post deposition annealing, the bi-layer displayed opto-electrical properties superior to that of the individual i-ZnO and IOH layers. The highest electron mobility achieved for the bi-layer was 103,70 cm^2 /Vs with a carrier density of 0,3*1020 carriers/cm^3. The working principle is the capping effect which i-ZnO has on IOH, keeping hydrogen contained within the bilayer during annealing. Further investigation will lead to additional information on the behaviour of hydrogen within the as deposited bi-layer in comparison to the annealed
one.

While the renewable energy sources are rising more and more throughout the years, and the effects of climate change starting to become more visible in our everyday life, some actions need to be taken. Combining different renewable energy sources gives the opportunity to build systems that can help limit these effects and provide energy in different types. The main goal of this project is to model a system that can offer electricity and hydrogen to a steel industry, in this case Tata Steel, and provide an insight for their next steps towards sustainability not only to cover their electricity needs but also investigate alternative steel making routes for their primary processes which are the iron making and further the steel making with hydrogen injection. The models developed for this project aim to answer the following research question: ”What is the feasibility to cover with a solar - wind - hydrogen system, the loads of the different steel making routes of Tata Steel ?” Different models were build through the software TRNSYS for the scenarios investigated that are linked with different combinations of components and loads so more sustainable steel making routes can be followed in the future. The steel making routes refer to the iron making process and the electrification of the industry with green electricity. For the year of 2030 a fuel mix of 70% natural gas and 30% of hydrogen and for the year of 2050, 100% of hydrogen will be used for the iron making process while for both of them 100% of the electricity loads were investigated to be covered by renewable energy sources. The scenarios were divided in a combining structure of local - non local generation and the loads corresponding to the different steel making routes. The local scenario refers to generation in the Netherlands while the non local scenario refers to the generation of hydrogen in the Arabic Peninsula and the generation of the electricity loads of the processes in the Netherlands. The components that were used were wind turbines, solar panels, batteries and electrolyzers. Each system was optimized with the help of GenOpt, an add - on of TRNSYS, to which was set to minimize the levelized cost of electricity, considering also the load coverage both for the hydrogen and electricity loads not to deviate more than 1% from the full coverage. Further than the optimization, a sensitivity analysis with the Sobol method through the programming environment of python and more specifically the SALib library and the parametric analysis of TRNSYS was conducted for all the different scenarios investigated to give an insight how the amount of the different components affects the levelized cost of electricity. Combining different metrics that were calculated as the Levelised cost of electricity (LCOE), the Self Sufficiency Ratio (SSR), the SSR of hydrogen, the total cost, the avoided emissions per MWh, the area ratio and the avoided emissions per area, a final comparison was done through the different scenarios. The most attractive choices both in a feasibility and economical perspective were the scenarios for local generation of hydrogen and electricity for the projected steel making routes of the years of 2030 and 2050. For the local generation scenario of 2030 an LCOE of 0.383 AC/kWh with an electricity coverage of 99.007 % and a hydrogen load coverage of 99.135% were resulted. On the other hand, for the scenario of the local generation of 2050, an LCOE of 0.421 AC/kWh, with an electricity load coverage of 99.875% and a hydrogen load coverage of 99.207% were calculated. The scenario that was the most attractive throughout the different metrics was the one for the local generation of 2050 while the next to come was the one for the local generation of 2030. Given the aforementioned study and its respectful results, it is a first step to evaluate the impact that such a system can have not only in the emissions reduction of such an intensively emitting industry but also to bring into perspective all the different aspects needed to be considered to realize such a project and evaluate them in more depth in the future.