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.

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.

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.

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.

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.

The future of our energy supply cannot continue to depend on the use of exhaustible fossil fuels. The successful transition to a society powered by renewable energy sources is one of the major challenges our current generation faces. Renewable systems will only fully establish themselves if high conversion efficiencies can be obtained at a reasonable cost, in order to compete with conventional, carbon-based sources. With this in mind, photovoltaic solar energy can be a promising solution.
This study focuses on the investigation of the potential efficiency of a thin-film tandem solar cell, combining amorphous silicon and microcrystalline silicon for a high performance device. With the use of flexible, light substrates, inexpensive modules can be manufactured in a roll-to-roll configuration to produce high efficiency products for a large scale implementation in society. The semiconductor modelling software ASA was used to optimise the structure of the tandem, identifying the absorber layer thicknesses that maximise the efficiency. Moreover, the impact of possible optical variations in the design of the device on the performance were analysed.
To start, model parameters of single-junction amorphous silicon and microcrystalline silicon cells were calibrated to recreate the performance of such devices based on experimental data. By conducting a sensitivity analysis of the model parameters, this was effectively achieved. The single-junction models were combined in a tandem structure to forecast the operation of the multi-junction device.
It was found that the performance of the tandem was highly sensitive to the choice of refractive indices of the layers at the junction between the two subcells. A high mismatch
between the refractive indices of these layers and the absorber layers of the subcells results in an increased reflection of light to the top cell. This is beneficial for the current production of this subcell, but is too detrimental for the operation of the bottom cell. By bringing the refractive indices closer together, an efficiency of 13.0% was predicted. The inclusion of an encapsulation at the front of the cell boosts this efficiency to 13.7%, at a top/bottom absorber layer thickness combination of 160 nm/0.6 µm.
The possibilities of enhancing the efficiency with an intermediate reflector were examined. The optical conditions for the ideal light distribution with such a reflector were
computed to provide estimations of the potential increase in performance. For the best performing device, an increase of the initial efficiency of 13.0% to 13.2% was foreseen, at slightly thinner top cells and similar bottom cell thicknesses.
All in all, the predicted efficiencies of the amorphous silicon/microcrystalline silicon tandem solar cell evidences the potential of these devices for the production of cheap,
highly efficient modules. The developed analysis of the ideal intermediate reflector can be generalised to other multi-junction solar cells to establish the potential efficiency increase such a layer brings along. This can help in the decision of whether the increase in performance justifies the added manufacturing complexity and costs.