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. ... Read more

The world is in need for an energy transition from the usage of fossil fuels to renewable energy source to reduce the harmful effects climate and health. Focusing on accelerating the research and development of photovoltaic technologies is an important step towards energy transition. The thin-film silicon solar modules has shown a great potential and a high market prospect. It is flexible, light-weight and also has a low manufacturing and installation cost. It is used for solar pumps and building integration. However, the highest initial conversion efficiency for a micromorph is 14.8%. Thus, we focus on further optimizing the multi-junction solar cells to reach higher efficiency by focusing on the improving the p-layer, texturing and silicon oxide intermediate reflector(SOIR). Further, standardized and error-free external quantum efficiency (EQE) measurement was done to obtain reliable Jsc values.

This work introduces deposition of single, micromorph and triple-junction thin-film solar cells on glass and wafers. The experiments were designed to study the effects of varying the material, thickness of the p-layer and n-SiOx reflective layer and textures of the solar cells. The Jsc from the EQE, Voc, FF and efficiency were the main parameters used to analyze the results.

The Jsc from the EQE measurement was not reliable as the EQE had an artifact while measuring micromorph devices. It was solved by increasing the bias light intensity and decreasing probe light intensity. The forward voltage bias was also found to be important for a cell with low shunt resistance and to measure the target cell in short circuit condition. The standard bias lights to be used are 1-3 to bias the top cell and 7-8 to bias the bottom cell combined with 50% reduction in the probe light intensity.

After correcting the EQE, the optimization of the top cell p-layer was performed on a-Si single junction solar cells on Asahi substrates. It was found that both the contact layer and the window layer of the p-layer have a high influence on the performance of the solar cell. A maximum conversion efficiency of 10% and Voc of 910mV were achieved for the a-Si single junction solar cells. Further, it was also found that there is more than one way to reach high efficiency with an optimal p layer by changing the material composition and thickness of both the contact and window layer. Additionally, p-SiOx contact layer resulted in good performing solar cells for larger range of F_B2H6 of the window layer than p-nc-Si contact layer and the insertion of the buffer layer in the i/p interface showed no significant improvement in the performance of the solar cell.

Furthermore, comparison of the performance of textures of different feature sizes was done on solar cells in p-i-n and n-i-p architecture. It was found that the best optoelectronic performance was obtained from asahi and smooth pyramidal textured solar cell in p-i-n and n-i-p configuration respectively in both double and triple junction solar cell. Further, the honeycomb textured substrate with R_rms around 270nm is not suitable to deposit on double and triple junction solar cell as it resulted in shunted cells.

Finally, the SOIR can be used in a-Si/nc-Si/nc-Si triple junction solar cell to divide current within middle and bottom junctions. The reflection of light in the infrared region increases with the thickness of the SOIR layer. A thick 90nm n-SiOx layer with F_B2H6=3.2sccm gives the best electrical performance and current distribution property for a micromorph. ... Read more

With an increase in population, there is increasing pressure and higher demand in world energy production. Even though there is a high dependency on fossil fuels renewable energy usage has seen a sharp rise in recent years. Solar energy is a major player and contributes a lot to this field. The thin-film solar cell which is a part of second-generation photovoltaic technology is faster and easier to manufacture. What makes them even more desirable is that they are lightweight, cost-effective, and can be manufactured by roll-to-roll production. The transparent conductive oxide layer acts as a front contact for a solar cell and thus plays a major role in guiding the incident light towards the active layer. This TCO has to be deposited on the aluminium foil to utilize its high conductivity and transparency in the active wavelength.
This thesis is part of the FLAMINGO PV (Flexible Lightweight Advanced Materials in Next Generation of Photovoltaics) project with collaboration between HyET Solar B.V and TU Delft. Aluminium foil is used by HyET solar as a substrate for TCO deposition. The bare aluminium foil has high roughness values and imperfections due to the presence of milling tracks and pinholes. The objective of the thesis is to do structural and optoelectrical characterization on this substrate foil and TCO using different process methods.
Bare aluminium foil received by HyET solar which was pre-treated showed a higher roughness value when compared with the untreated samples. This also provided good correlation data with one of the supplier companies. Morphological analysis showed 2020 factory baseline samples having more milling tracks and pinholes compared to 2021 factory baseline samples. The pre-treated sample showed the presence of precipitants which was not the case in untreated samples. FLAM02 textured aluminium foils showed higher roughness values when compared to the 2020 and 2021 factory baseline but this has an overall better impact on its optical property. For Al + TCO samples structural characterization showed the presence of milling tracks and pinholes. Using a scanning electron microscope the optical thickness of TCO was confirmed. For TCO + Carrier foil fewer milling tracks were noticed while characterizing them with SEM and 3D confocal microscope.
Optical characterization for the textured sample shows a similar value in diffused reflectance between the 2020 and 2021 factory baseline and a small increase in specular reflectance for 2020 factory baseline samples. FLAM02 textured samples showed a higher value in diffused reflectance and haze as compared to factory baseline 2021 and FLAM01 textured samples. Electrical characterization done on TCO + Carrier foil where a low free carrier concentration and high mobility is desired.
... Read more

Our world is on its way to re-engineer the daily life based on renewable clean energy. And this multilateral attempt to combat environmental and climate change has its focus perfectly poised to embrace the infinite energy source - solar energy as an alternative. Thin-film photovoltaic technology also referred to as second-generation technology is an alternative family of solar technology in the market which holds rich market prospects such as potential advantages of cost-effective substrates, low transportation-installation costs due to its lightweight property and the possibility of direct integration in building materials. HyET solar is focusing its production on Roll-to-Roll manufacturing of thin films. The utilisation of R2R production with efficient deposition in substrate configuration, and the serial interconnections of cells done during production can bring down the cost of production and contribute to manufacturing flexible solar cells on polymers. The thin-film solar energy technology is looking at a possible re-entry to the market with these advantages. Integrating the micromorph configuration into this technology is challenging. To start we have taken two base models and tried to fabricate tandem samples on the aluminium substrate. These substrates are temporary foils with modulated surface texturing implemented on them for better light utilization. The initial lab-scale samples yielded less than 35%of the total. The lab-scale samples showed highly defective μc-Si :H subcells. An investigation on the layers used in the samples was conducted and it suggested conclusively that the μc-SiOx n layers with low activation energies were the main reason for the very low shunt resistances in the cells. The power of optoelectronic modelling is taken advantage of to improve the performances is done. This study resulted in a model of optimised efficiency of 12.2%. A study on doping of the tunnelling recombination junctions suggested that with poorly doped layers, the objective of TRJ to facilitate tunnelling recombination at the junction is not satisfied and ultimately affect the cell behaviour forming a reverse biased n-p junction. The use of a highly reflective intermediate reflective layer for the tandems is detrimental to the bottom cell performance. But at the same time, a reflective behaviour in the TRJ p-doped layer, when using a p-doped μc-SiOx layer fabricated at 3.2 sccm CO2 flow rate, the reflection is moderate and can be proved beneficial resulting in a thinner top cell. The possibility of modelling to predict the performance, out of standard test conditions suggests a drop in the open-circuit voltage of our cell by 4.9mV per Kelvin increase and a fall in the efficiency by 0.058% per Kelvin.
In summary, the tandem flexible solar cells once overcome the challenges in fabrications, it can facilitate cheap, high-efficiency modules. The simulations on this same structure point towards several potential spaces for the micromorph configuration for improvement within itself and certainly a bright future ahead of us powered by thin-film flexible tandem solar cells.
... Read more

The use of clean energy sources for meeting the world’s energy requirements is increasing at an exponential rate, thus opening up new areas for research and development. The second generation of photovoltaics, especially flexible thin-film solar cells, are increasingly being used over the first generation crystalline silicon technologies due to their lightweight, flexibility, low cost, and decent efficiency. The low cost is possible mainly as a result of using a thinner absorber layer compared to crystalline silicon technologies. However, the thin absorber layer mandates the use of efficient light management techniques in order to increase the solar cell performance, as otherwise, the thin absorber layer will lead to very low photon absorption. Modulated surface texturing is one such light management technique where different textures are introduced at different interfaces and finally stacked together in order to superimpose various scattering mechanisms, thus increasing the optical path length of light. The modulated surface texturing principle has two goals: first, to provide efficient light trapping, and second, to promote the growth of smooth & dense high-quality nc-Si layers. 
HyET Solar B.V. is a company located in the Netherlands that uses state of the art roll-to-roll technology to manufacture flexible thin-film silicon solar cells. This thesis is a part of the ongoing FLAMINGO PV project in collaboration with TU Delft and HyET Solar B.V, to develop tandem & triple-junction solar cells with high efficiency & lifetime. HyET Solar B.V. uses an aluminum foil as a temporary substrate on which the TCO and subsequent solar cell layers are deposited. The goal of this thesis is to implement optimized modulated surface texturing for the solar cells developed at HyET Solar B.V, by creating ’U’ shaped micro-sized craters on the aluminum foil and subsequently depositing ’V’ shaped, naturally nanotextured FTO on it. The microtextures are created on the aluminum foil by the process of wet chemical etching, where the three main etching parameters- temperature, concentration, and time are varied in order to obtain the most suited recipe. An alkaline-based etchant (NaOH) is used for the wet chemical etching process. The textured features on the aluminum foil are analyzed for its morphological and optical properties. The morphological analysis using a 3D laser scanning microscope & SEM helps in obtaining the surface roughness properties while the optical analysis using Integrating sphere and ARTA helps in measuring the light scattering effectiveness. To ensure the mechanical stability of the roll-to-roll machine, a minimum foil thickness of 95μm is required after etching. Taking this as the first requirement, the etching recipes were varied and optimal results were obtained when the aluminum foil was textured with 60g/L NaOH at 60°C for 2.5 mins (NaOH60) and 60g/L NaOH at 70°C for 1.5 mins (NaOH70). Further analysis showed that texturing using NaOH60 resulted in better surface roughness and scattering properties compared to the aluminum foil textured with NaOH70, and it was thus chosen as the optimal recipe. This optimized recipe is known as FLAM02. 
 The TCO leak tests at HyET Solar B.V. showed that the aluminum foil contains pinholes & milling tracks, which are further enhanced after texturing using the factory baseline and FLAM01 process. Initial results showed that annealing the foil before texturing leads to a reduction in pinhole density & surface roughness caused due to milling tracks. Experiments were designed to validate this where the two annealing parameters - temperature and time were varied. The aluminum foils were textured after annealing using the factory baseline, FLAM01, and FLAM02 processes. Morphological analysis, which was conducted before and after texturing, showed that annealing the foil before texturing does not lead to a decrease in pinhole density and surface roughness due to the milling tracks. The optical analysis using laser scattering validated this. One observation was that texturing using the FLAM02 process led to the significant amount of aluminum foil being etched away, thus resulting in the reduction of milling track roughness and pinhole density. ... Read more

Photovoltaic (PV ) technology has seen exciting growth in the field of energy for the past few decades. With strong government programs in China, Japan, Germany, and Netherlands, PV systems have grown to become a dominant source of renewable energy. Thin film silicon based a-Si:H solar cells are 2ndgeneration solar cells. They have the ability to be applied on glass or polymer, free of toxic materials in the manufacturing process, and are extremely flexible. Even though they exhibit a lower efficiency with respect to other proven technologies, a lower temperature coefficient and the unique ability to self-anneal in warmer months make it an attractive option. HyET Solar Netherlands B.V. manufactures thin-film solar cells based on a-Si:H technology. These modules are extremely flexible and relatively cheaper to manufacture, hence are suited for Building Integrated Photovoltaics (BIPV ) setups in the form of soundwalls, curved roofs, and solar blinds among many others. The primary aim of this research is to understand the performance variation of the solar modules when they are not under Standard Test Conditions (STC) but are aged outdoor. To understand this, data was collected from solar modules installed outdoor. The installed PV system consists of 16 arrays, each array comprising of two modules connected in series and each module consisting of 28 cells in series. However, during installation, some of the modules were damaged, and analysis was solely done on the best-performing array. To analyse the system, irradiance, temperature, and operating maximum powerpoints(mpp) were recorded every minute while the JV-curves were measured every fifteen minutes. The modules were analysed on two levels: on the system level and the cell level. Analysing the modules on system level was done by calculating the performance ratio and daily energy yield. It was found that the modules performed significantly better in warmer months than in cooler months. This could be explained by a combination of the annealing effect and relatively lower losses due to higher irradiance in warmer months. Upon analysing the daily energy yields of the modules, it was found that the system suffered degradation of 10.3% in the second year of operation. To analyse the modules on the cell level, JV-curve data were used. To extract the intrinsic parameters of the modules from a JV-curve, an in-house software "DoktorDEP" was utilised. In order to validate the output from the software, two experiments were performed, where JV-curve were measured at different temperature points and irradiance. While the experiments were successful in estimating the intrinsic parameters, certain requirements were not met at the outdoor data, hence the focus was now shifted to explicit JV-curve parameters such as short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), open-circuit resistance (Roc) and shot-circuit resistance (Rsc). Upon analysis, it was found that there was a Jsc loss of 0.63mA/cm2 and Voc loss of 0.02V/c in the second year of operation. Moreover, the ontained trends of FF and Roc exhibited a definite degradation while the Rsc did not exhibit a degrading trend. Even though data analysis was performed on damaged modules, the obtained trends in this study can be of vital importance in developing strategies for reliability of the modules. The same techniques can be applied to a set of undamaged modules to estimate the performance. Because the JV-parameter Roc was affected drastically as the modules aged, future experiments can be designed to observe and tweak Roc to improve both efficiency and reliability. Lastly, based on the insights about DoktorDEP, future versions can be rolled out with the ability to analyse outdoor JV-curve data to discern the intrinsic parameters and their variation when aged outdoor. This could help in targeting and prioritising the factors affecting module performance and hence resulting in a robust product. ... Read more

Thin-film flexible solar panels can be utilized on many surfaces where conventional solar panels are hard to be used such as side walls of buildings, ship roofs or curved surfaces. In conventional solar cells, glass is used to protect the panels from external damage. However due to its heavy weight and rigidity, glass is not an option for thin-film flexible solar cells. HyET Solar, a company based in the Netherlands that produces flexible thin-film solar cells uses a transparent foil produced using a roll-to-roll process to encapsulate and protect their solar panels. In order to reduce the amount of materials used and cut the costs, a thinner foil is being developed. Producing the thinner foil in a roll-to-roll process causes different defects in the foil, among which half sinusoidal waves forming mostly in the bottom side of the foil, these waves are called wrinkles. The process of manufacturing the top encapsulant layer involves changing temperatures and mechanical stresses applied on the foil. Therefore, two models were developed to understand the effect of three process parameters (web force, web speed and temperatures of each production zone) on wrinkle formation. First, a thermal model of the process using ANSYS program was developed to understand the temperature profile of the produced foil along the process. Then, a mechanical model that uses the output of the thermal model and the applied mechanical forces to study the effect of the investigated production parameters on wrinkle formation was worked out. The results show that operating at higher temperatures and reducing the thickness of the foil are directly responsible for decreasing the threshold of the critical stress that causes wrinkle formation and thus reducing the range and the magnitude of the force to 1.4 N is needed to perform the process without forming wrinkles in the foil. Varying web speed between 0.3 m/min and 3m/min is found to have a minor effect when varied under high temperatures. Finally, decreasing the temperature of the first and second zones by 10 °C is found to extend the range of the web force that can be applied. Performing the process under lower temperatures or reducing the mechanical forces that act on the foil will reduce wrinkle formation in the developed foil; web speed should not be considered in mitigating wrinkle formation. ... Read more

Individual actions cannot solve the current climate crisis. Part of the collective effort is to research solar energy as new ways to produce cleaner, cheaper and more efficient electricity. Among all the current solar cell technologies, a thriving and promising one is perovskite as an absorber material. In the last ten years, the power conversion efficiency evolved with a steep rhythm. In 2019, a maximum of 25.2% in a single junction configuration was reported, while more actual research proves that using them as a tandem can reach up to 30%. Perovskites have the advantage of changing their bandgap by ion-­mixing, from as low as 1.2 eV to even higher than 2.5 eV. Besides, it is flexible, translucent and has similar efficiencies to c­-Si; while being cheaper and easier to produce. It is expected that it will replace c­-Si-­based solar cells in the long run and significantly reduce the price of solar energy.

This project is developed under the Photovoltaic Materials and Devices (PVMD) section of TU Delft, in conjunction with HyET Solar and Flamingo PV. The software ASA and GenPro4 were used to validate single-­junction solar cells and optimize tandem devices. The goal of this thesis is aligned to HyET’s ob­jective: improve its flexible thin-­film solar cell by increasing the power conversion efficiency above 12%.

To carry out the validation and calibration of the single­-junction references, first, a study of all the possible perovskite­-based solar cells was performed. The chosen perovskites have a Methylamonium and Formamidinium combination. The first one has a bandgap of 1.55 eV and works as a high bandgap
absorber material (K0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3), while the low bandgap corresponds to 1.25 eV ((FASnI3)0.6(MAPbI3)0.4) [20]. By adjusting some of the absorber layers’ electrical parame­ters, the references’ electrical properties were matched.

Once validated, the respective p­i­n junctions of the perovskite solar cells were introduced into HyET’s solar cell architecture. By doing this, it is already possible to see the advantages of using per­ovskites as absorber materials: the power conversion efficiency grew from 7.71% to 18% and 19.45% for the high and low bandgap cells. Besides, there is also a better use of the light spectrum. Cali­brating a tandem solar cell is much more complicated. That is why it is done first on the individual single-­junction solar cells, and afterwards, both are stacked together.

The first step to optimize a tandem device is to do an optical simulation (GenPro4). By analyzing the absorptance of the tandem device and the optical current of the top and bottom absorber materials, it is possible to obtain the best combination for the current matching of the tandem solar cell. By modifying
both of the absorber materials’ thicknesses, the optical current mismatch can be reduced. As a result: 300 nm and 600 nm thickness for the a­-Si / LBG perovskite tandem, and 120 nm and 1700 nm for the HBG perovskite / nc-­Si; achieving a mismatch below 0.04 mA/cm2 and 0.2 mA/cm2 correspondingly.

The second step in optimizing a tandem device involves an electrical simulation (ASA). The optimization is related to facilitating tunneling recombination at the n­-p junction by adjusting the doping of these layers. The optimized tandem solar cells have the following electrical properties: 1.56 V, 14.54 mA/cm2, 0.85 and 19.69% for fill factor and PCE for the HBG perovskite / nc-­Si tandem solar cell; while 1.55 V, 11.13 mA/cm2, 0.72 and 12.36% for fill factor and PCE of the other. With these results, it is plausible to confirm that HyET’s objective of having thin-­film flexible solar cells with a PCE above 12% can be met by using perovskite technology in their production line. ... Read more

Given the rising research of thin film solar cells in recent years, flexible technology has been proven to be more light weight and cost effective. As photovoltaics is increasingly becoming the front runner in sustainable energy production, concerns over the associated impacts of solar modules throughout their life cycle are also increasing. This study quantifies the environmental impacts through LCA analysis for Roll-to-Roll (R2R) production process of thin film flexible silicon-based solar modules manufactured by a Dutch company HyET in The Netherlands.

This study considers three product lines over a life cycle demarcated into its manufacturing, encapsulation and installation. The three product lines (cases) are as follows.
1. Single junction a-Si with 7% efficiency.
2. a-Si/nc-Si tandem cell with 10% efficiency
3. a-Si/nc-Si tandem cell with 12% efficiency
The installation phase considers a rooftop setup of capacity of 2.1 kWp with Balance of System (BoS) components.

LCA analysis is carried out on Simapro 9.1.0.11 following the guidelines and the framework of International Organization for Standardization ISO14044. The outcome of LCA analysis is measured in terms of Global Warming Potential (GWP), Primary Energy Demand (PED) and Energy Pay Back Time (EPBT). Ecoinvent 3.5 is used as the primary database for these analyses to select the inventory. GWP is assessed using the CML-IA baseline method while PED is assessed using Cumulative energy demand v1.11 method. Sensitivity analysis is done by changing the location of production and up-scaling capacity.

The installation stage is observed to contribute the highest GWP and also has the highest PED on account of BoS components. The LCA analysis has demonstrated similar trends of GWP, PED for all three product lines. EPBT on the other hand, is longer for 10% tandem cell on account of relatively larger module area as compared to 12% tandem cell and also the relatively higher energy consumption as compared to the single junction cell. The choice of substrate material is seen to impact the assessment indicators significantly. Flexible glass is observed to be the optimal choice for large-scale production. The choice of encapsulant material also affects the indicators demonstrably. Sensitivity analysis shows a positive impact on the indicators through up-scaling, while the location is not established as a significant factor sufficiently under considered assumptions. ... Read more

Thin-film photovoltaic technologies are gaining momentum over the currently dominated crystalline silicon technologies. In addition to the competitive prices, flexible thin-film technology especially has the added advantage such as in building integrated photovoltaics (BIPV) due to its flexibility and light weight. HyET Solar B.V. is a company based in the Netherlands which state-of-the-art Roll to Roll (R2R) technology to produce such flexible solar cells. A temporary aluminum foil is used as substrate on to which FTO/p-i-n 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 on-going 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. This thesis is inspired by the work of Tan et. al [8] where record efficiency cells were achieved on solar cells deposited on ‘Modulated Surface Textured’ (MST) glass substrates. In MST, increased light scattering is obtained by superposition of various scattering mechanisms which is achieved by introducing different textures at different interfaces and stacking them together. The requirements of the MST are two-fold: to provide efficient light trapping and to aid in the growth of high-quality layers. The aim is to introduce MST in the R2R process by developing micro sized crater-shaped features on the temporary Al foil on to which naturally nano sized V-shaped textures of FTO is deposited. The crater-shaped features are developed on the Al foil (~110 um) using wet chemical etching techniques. Various acid and alkaline based etchants are experimented. The etching parameters- concentration and temperature of the etchant and the etching time are varied to achieve the optimum recipe. These parameters should be varied such that the features have a correlation length (an estimate of how wide the feature is) 3-4 um and an aspect ratio (ratio of RMS roughness to correlation length) of 12-14%. These features are characterized using SEM and AFM to measure the aforesaid parameters and reflectance and angular intensity distribution measurements to measure its effectiveness of scattering. Alkaline based etchants (KOH and NaOH) resulted in crater-shaped features unlike acid etchants which resulted in pyramidal features. It was observed that there is an initial ‘induction period’ before which the etching started. For lower temperature, time and concentration, the induction period is longer. To ensure mechanical stability during deposition stages, the foil needs to be thicker than 70 um on lab-scale. The above-mentioned etching parameters were varied, and the best recipe was found to be 1.78M KOH at 70°C for an etching time of 2 minutes, 1.78M KOH at 60°C for 3 minutes and 1.42M NaOH at 70°C for 2.5 minutes. These samples displayed a correlation length 4-4.6 um and aspect ratios from 12-14% which is close to the targeted values and are higher than the existing texturing at HyET (‘factory baseline’) which had correlation length and aspect ratios of 500 nm and 5.7% respectively. These samples also showed higher scattering compared to the factory baseline. The nc-Si:H and a-Si:H/nc-Si:H layers deposited on to these samples resulted in dense high-quality layers. The TCO/p-i-n layers deposited also adapted the texturing pattern of the Al foil, unlike the factory baseline where the Al surface morphology was not adapted by the other layers as the features were significantly smaller. Further, to enhance the uniformity of texturing, various ‘chelating agents’ and ‘surfactants’ such as gluconic acids and glycols as well as varying the speed of etching to ensure homogenous contact of etchant with the foil was carried out. Both these techniques resulted in in an increased etch rate as well as an increase in the density of the craters on the foil. Considering the limitations of the R2R process, the best lab recipes were adapted (50°C, 1.42M NaOH, 1.8 minutes) to implement on the R2R etching machine. The resulting Al foil had higher surface morphology parameters and scattering compared to the factory baseline. The cells deposited on this texturing adapted the morphology of the Al foil. Optical simulations were done using GenPro4 where the AFM data of the textures were given as the input. The best lab samples as well as the R2R testing recipe showed larger absorption in the higher wavelengths in both nc-Si:H single junction and a-Si:H/nc-Si:H tandem cells, compared to the standard factory baseline texturing. ... Read more

Thin film amorphous silicon based PV systems are a rather new and promising photovoltaic technology with plenty field for technological development and potential for unique applications such as integration within the built environment. Nevertheless, in order for the technology to be established, further technical development is required and economical aspects should be tackled, both in the module and system level. From a commercial point of view, the ultimate goal of a PV system, once installed, is to cost effectively deliver the highest possible energy yield. In reality, the actual energy yield every system delivers is lower than the theoretical rated performance. Location and environmental factors, such as heating of the modules, irradiance, dirt accumulation, angle of incidence, Etc. affect the performance of the systems. Understanding the behavior of this new technology under real operation conditions can provide reliable insights for its further development, help better estimate the energy yield amorphous silicon systems can provide and perhaps, help the technology differentiate itself from the better commercially established crystalline silicone based one. This work investigates the effect of most of the location and environmental factors affecting the performance and the ultimate energy yield of a photovoltaic system comprised of flexible and lightweight amorphous silicon modules. The factors responsible for this performance decrease are individually investigated, and its effects are quantified by addressing in which manner they decrease the performance ratio of the system. A performance monitoring system was built expressly for this purpose, which data acquisition plan was based on the IEC 61724 -1 (2017) standard. A computer model with the capability of simulate the performance of the system after correcting for the evaluated mechanism was also constructed as part of this work using Matlab. This model was based on an experimental characterization of the modules, using live performance data as an input to give a performance ratio, and an assessment of the effect of loss factors. The results allocated the source of the system losses up to a 78% of the total power decrease, considering the rest of the unexplained observed losses as effects of the active material degradation. The performance ratio of the system was reported on a daily bases for the full evaluated period, concluding a strong correlation between a high irradiance and a high performance ratio. The common literature claim of a better behavior of thin film a-Si:H technologies compared to c-Si was verified under this study, and the effects of system operation under low irradiance conditions was identified as the dominant loss mechanism. ... Read more