High conversion efficiencies and low production costs have placed Silicon heterojunction (SHJ) solar cells as one of the top contenders in the photovoltaic market right now. When combined with the interdigitated-back-contacted (IBC) architecture, SHJ-IBC cells set world record efficiencies for silicon cells: in 2024, the record stands at 27.3% efficiency. However, the IBC architecture introduces complex processing steps. The goal of this project is the simplification of processing steps of SHJ-IBC solar cells, obtained with the use of hard masks for the direct deposition of patterned layers.

The first part of the project is focused on the development of hard masks. First, silicon based hard masks have been fabricated using wet and dry etching methods. Their fabrication process has been optimized until high quality masks with low defect rates have been achieved. In addition to these masks, quartz mask samples provided by a third party have been tested. Deposition of 50 and 100nm of (n) nc-Si:H have been made with all masks to evaluate their potential based on their resolution, quality, reusability and price. While quartz masks have demonstrated to be very promising and industry orientated, the best trade-off of qualities in a research environment has been found in dry etched silicon masks.

In the core of the project, dry hard masks have been used to substitute two photolithography steps in the fabrication flowchart of IBC-SHJ solar cells in order to achieve a significant process simplification. The use of hard masks has brought relevant impacts to the SHJ-IBC cell fabrication, like the removal of wet etching steps that can potentially bring uncertainty to process flowchart and the reduction of the processing time to half of what it was before the use of hard masks. Regarding the depositions made through the hard masks, the challenges of obtaining a precise alignment and accurate feature sizes been assessed. The implication of those challenges in the performance of the solar cells has been then evaluated.

Lastly, the thesis introduces a simplified fabrication process of SHJ-IBC solar cells with the implementation of hard masks. With the new fabrication process, efficiencies of up to 5.47% have been demonstrated. Through the introduction of the SHJ-IBC flowchart based on hard mask patterning, the project contributes to the ongoing effort to bring SHJ-IBC cells closer to the industry.

The installed capacity of photovoltaic (PV) technology has increased beyond expectations and is expected to grow even more. One of the most promising PV technologies currently dominating the PV market is the silicon heterojunction (SHJ) solar cells, which hold the highest c-Si single junction efficiency of 27.3% in an interdigitated-back-contacted design. To achieve such high efficiencies, an optimized (i)a-Si:H passivation layer is of great importance. This thesis aims to scale up the lab baseline SHJ technology by optimizing large-area c-Si surface passivation with hydrogenated intrinsic amorphous silicon (i)a-Si:H layers. In view of the development of high-efficiency perovskite/c-Si tandem solar cells, this thesis also covers the development of nanotexture on crystalline silicon (c-Si) wafers used for the bottom cells.
The research for optimization of large-area c-Si passivation with (i)a-Si:H layers first started with obtaining recipes that would deposit uniform (i)a-Si:H layers over M2-sized glasses. The deposition conditions of plasma-enhanced chemical vapor deposition (PECVD) were optimized and various promising recipes that delivered highly uniform (i)a-Si:H layers were obtained. No statistically significant correlation was found between the deposition parameters and the uniformity of the (i)a-Si:H layers.
The passivation quality of the (i)a-Si:H layers was assessed by symmetrically depositing the (i)a-Si:H layers on c-Si wafers and measuring the lifetime. For single-layer passivation strategy, (i)a-Si:H layers prepared with the highly hydrogen-diluted silane (SiH4) resulted in relatively low lifetime values, potentially due to epitaxial growth, while layers deposited with less hydrogen-diluted SiH4 or pure SiH4 resulted in better lifetime values. The best lifetime achieved with single-layer passivation was 8.23 ms. Furthermore, utilizing a bilayer concept that first deposits an ultra-thin (i)a-Si:H layer with pure SiH4 and then stacks on its top a highly hydrogen-diluted (i)a-Si:H layer, can enhance the passivation quality over their single-layer counterparts. With proper selection of the (i)a-Si:H layers that compose the bilayer and the optimum thickness combinations, a lifetime of 16.10 ms was achieved. Moreover, the passivation quality can be further boosted by applying a hydrogen plasma treatment (HPT) of 30 seconds on top of the optimized bilayer. HPT durations longer than 30 seconds resulted in a decrease in lifetime, possibly due to the oversaturation of hydrogen that leads to defect formation. A lifetime as high as 21.53 ms was obtained by combing the bilayer approach and a HPT.
Last but not least, the creation of nanotexture on c-Si wafers was done by anisotropic etching, using KOH, KsSiO3, and surface additive monoTEX 2.6. By varying texturing conditions, namely, temperature and duration, various surface morphologies of c-Si wafers were obtained. According to SEM characterizations, pyramidal features below 1 μm were successfully created mainly thanks to K2SiO3 slowing down the etching rate during the texturing process. The lowest reflectance was obtained by etching the c-Si wafers at 70 °C for 20 minutes. It was also found that K2SiO3 has an extremely slow dissolving rate and the most effective way of dissolving K2SiO3 is by adding KOH and K2SiO3 to DI water at room temperature and heating it to 80 °C while mixing.

Global warming is currently being regarded as one of the most significant concerns in society. As globalnwarming is related to the greenhouse gases emitted from the current energy supply, there is a needbfor renewable energy sources. Solar energy is an energy source which has zero emissions and could
in theory supply the energy demand. A solar cell is technology based on the photovoltaic effect, it converts solar irradiance, specifically the energy derived from photons, into electrical energy. Over the course of the development of photovoltaic technology, numerous variations of solar cells have been introduced. By IRTPV, it is anticipated that new and advanced concepts, especially the Tunnel Oxide Passivating Contact (TOPCon) solar cell, will come to dominate the solar market in the coming years. At ISCKonstanz, the primary objective is to develop solar cells that are feasible for industrial applications.
The solar cell under investigation and exploration within the context of this particular thesis is referred to as TOPCon Rear Junction (TOPCon RJ), it differs from the well-documented TOPCon emitter Front Junction (FJ). The notable advantage lies in the fact that by placing the emitter at the RJ, the FSF can be
lightly doped, thereby reducing Auger recombination. Another advantage is the possibility of increasing the metal pitch between the fingers, reducing the metal used. Even more, the TOPCon RJ doesn’t need the high temperature boron diffusion needed for TOPCon FJ, because of doping during APCVD deposition. Simulation results indicate that TOPCon RJ can achieve at least the same
efficiency as TOPCon FJ. The TOPCon solar cell is developed on large area n-type Cz wafers, with a selective n++/n+ FSF of c-Si, a by APCVD inline deposited p+ poly-Si layer and screen printed silver contacts. The inline APCVD has fast processing as a major advantage. A comprehensive description of the TOPCon RJ solar cell structure will be provided. The solar cell’s parameters will be elaborated on, in order to characterize it. The report incorporates basic supportive solar physics. Various characterization methods will be expounded upon to offer a more comprehensive understanding of the research methodology. The research is divided into three parts: the development of the p+ poly-Si rear layer, the development of the n+ c-Si FSF, and the process of metallization. Good passivation for the individual layers were achieved and good contacting as well. However, viable cell results were not yet obtained. The research necessitates substantial further enhancements. Moreover, the presence of defects and damages significantly impacted the outcomes, lowering the reliability.

Climate change is real. Energy transition plays a crucial role in addressing climate change where solar fuels have emerged as a critical player in reducing the dependence on fossil fuels in industries that cannot transition into renewable electricity as an energy source such as aviation, industrial feedstocks etc. Green methanol is a promising solar fuel if it is sourced via carbon capture technologies. This thesis aims to build and use a model of an integrated methanol synthesis microplant as a tool to predict methanol production and the performance of the microplant under multiple system architectures at Zero Emission Fuels B.V (ZEF) who are developing a solar powered green methanol synthesis plant. The research commenced with data preprocessing which utilised historical weather data from the C3S database. Subsequently, individual subsystem models were developed such as solar photovoltaic (PV) modules, direct air capture (DAC), fluid machinery (FM), alkaline electrolysis cell (AEC), methanol synthesis (MS), distillation (DS), buffer tanks, and battery system. To ensure the microplant's functionality, a sophisticated control algorithm was devised, operating on two distinct levels: battery management and power distribution. Moreover, diverse microplant architectures were designed, to address unique operational scenarios and environmental conditions. The investigation further explored the influence of temporal granularity, and component sizing on microplant behavior. Ultimately, this thesis establishes the feasibility of the ZEF microplant, offering valuable insights for practical implementation across multiple locations. Consequently, it underscores the potential of the ZEF microplant as a promising solution in the transition towards sustainable energy alternatives.

Considering the rapidly growing energy demand in worldwide and climate deterioration caused by fossil fuel, the remarkable potential of solar energy has captured the attention of individuals and industries alike. Among different techniques, poly-Si based passivating contacts have shown great performance on solar cell application, which enabling a high efficiency of over 26%. Plasma-enhanced chemical vapor deposition (PECVD) as one of the promising technologies in a-Si contacting layer fabrication has gradually replaced the conventional LPCVD method in industry. However, the accompanied severe ion bombardment is not negligible, especially on its underlying fragile tunnelling oxide. In this work, the impact of PECVD a-Si:H contacting layer deposition on poly-Si/SiO_x passivating contact is investigated. 
PECVD radio-frequency (RF) power for the contacting a-Si layer on the underlying SiO_x is the only variable in this project, varying from 5 W to 55 W, and pinhole density acts as a bridge to help analyse the intrinsic principles. Firstly, the results of a-Si:H thin film characterization suggest that with an increasing RF power, the a-Si:H thin film is grown at a higher deposition rate and becomes porous. In addition, the pinholes in tunnel oxide are inspected by applying the concepts of “selective etching” and “pinhole magnification”. With a two-step five-point sampling method, it is shown that the effect of RF power on the pinhole density is not monotonically increasing. The highest value is found at 25 W. To explain this, a concept of “protective layer” is proposed, which is defined as a buffer layer (contacting layer) formed at the very beginning during a-Si:H deposition. It appears to be more effective when higher RF power (> 35 W) is applied. Another influence on tunnel oxide property is discussed according to the result from XPS measurement. The percentage of Si⁴⁺ species is found in the case of 25 W, corresponding to the highest pinhole density. This proves to some extent that the severe particle bombardment brought by strong power would weaken or directly break the Si-O bonds in the PECVD substrate, that is the tunnel oxide in our case.
As a result of thin film characterization, five factors contribute to pinhole formation: (i) Defects in tunnel oxide from imperfect oxidation leave potential for pinhole formation. (ii) Severe ion bombardments in PECVD deposition are allowed to weaken or break Si-O in SiO_x. (iii) Island growth of a-Si:H contacting layer makes the exposed region in tunnel oxide continue to be damaged. (iv) “Buffer layer” formation protects the substrate from ion bombardments. (v) The tensile stress applied by a-Si:H films during annealing intensifies the formation of pinholes. 
Subsequently, an unexpected result from passivation quality assessment is that higher passivation level is presented with higher pinhole density. The best passivation quality is found in the case of 25 W, with J₀ of 3.3 fA/cm² and iV_oc of 714 mV. Further, a large optimal process window for RF power adjustment is found from 25 W to 35 W, which leads to an iV_oc over 710 mV, with single side J₀ below 3.5 fA/cm². The results from specific contact resistivity indicate that it is positively correlated to the pinhole density. Eventually, the champion passivating contact with a selectivity of 14.37 in this project is expected to yield a maximum efficiency of 28.9% in an ideal c-Si solar cell.

Silicon heterojunction solar cells (SHJ) showed a record efficiency of 26.81%, approaching the theoretical limit of single-junction crystalline silicon (c-Si) solar cells. To further improve the efficiency, a wide bandgap perovskite top cell can be stacked on top of the SHJ bottom cell forming tandem solar cells, which utilize better the solar spectrum. Recently, a record efficiency of 33.70% was achieved for a monolithic two-terminal perovskite/SHJ tandem solar cell. Typically, a transparent conductive oxide (TCO) layer, functioning as the recombination junction, is used to connect the two sub-cells. However, tandem solar cells with this conventional TCO recombination junction often feature high reflection losses originating from the intermediate interfaces between the two sub-cells. Therefore, this master thesis focused on minimizing these intermediate reflection losses by substituting the TCO-based recombination junction with proposed TCO-free recombination junctions.

Firstly, comprehensive optical simulation studies that compared 2T tandem solar cells with various recombination junctions were performed. In the case of single-side-textured (front-side-flat) tandem configuration, as compared to the reference cell with tin-doped indium oxide (ITO) recombination junctions, the use of the more transparent tungsten-doped indium oxide (IWO) allowed an improved implied photocurrent density in the bottom cell (Jimp,bottom) from 18.30 mA/cm2 to 18.70 mA/cm2. Further, by using the TCO-free recombination junction composed of (p)nc-SiOx:H/(n)nc-SiOx:H or (p)nc-Si:H/(n)nc- Si:H, ranges of optimum thickness combinations were discovered, which allowed high Jimp,bottom values of 20.30 mA/cm2 or 19.80 mA/cm2, respectively. Both TCO-free recombination junctions demonstrated enhanced light coupling to the bottom cell thanks to the optimized interference effect at the intermediate interfaces between two sub-cells, minimizing the associated reflection losses. Furthermore, the designs of tandem solar cells featuring various recombination junctions were optimized to reach maximum matched tandem current density. For the reference cell with ITO recombination junction, a matched tandem current density of 19.40 mA/cm2 was obtained, while the use of TCO-free recombination junctions, for instance, 60 nm (p)nc-SiOx:H/ 70 nm (n)nc-SiOx:H or 30 nm (p)nc-Si:H/75 nm (n)nc-Si:H, demonstrated high Jimp,bottom values of 19.80 mA/cm2 and 19.80 mA/cm2, respectively. These results highlight the optical advantageous implementations of proposed TCO-free recombination junctions for monolith tandem solar cells. Similar observations but less significant improvement by using the proposed TCO-free recombination junctions were found in double-side-textured tandem solar cells. This is due to the already minimized reflection losses of the (p)nc-SiOx:H/(n)nc-SiOx:H or (p)nc-Si:H/(n)nc- Si:H configurations (1.3 mA/cm2 and 1.4 mA/cm2 respectively) as a result of the textured front surface.

Based on optical simulation studies conducted on 2T tandem solar cells, the electrical effectiveness of proposed TCO-free recombination junctions was examined by fabricating proof-of-concept single junction single-side-textured SHJ solar cells. First, we focused on the passivation optimization of the flat (100) c-Si surface as it is prone to detrimental epitaxial growth. An impressive minority carrier lifetime of 16.87 ms was achieved by combing (n)nc-Si: H and (i)a-Si: H bi-layer in a symmetrical configuration. Moreover, we also observed, in general, better conductivity when increasing thicknesses of doped nc- SiOx: H layers when they were deposited on glass or (i)a-Si: H coated glass substrates. Eventually, proof-of-concept single junction single-side-textured SHJ solar cells featuring the proposed TCO-free recombination junction were fabricated. According to the optical simulations, various optimum thickness combinations of (p)nc-SiOx: H and (n)nc-SiOx: H or (p)nc-Si: H and (n)nc-Si: H that composes the recombination junction were tested. Overall, the optically promising TCO-free recombination junctions in 2T tandem solar cells also delivered high FF values in proof-of-concept single-junction SHJ solar cells, demonstrating their potential to be implemented to fabricate high-efficiency monolithic 2T tandem solar cells.

The photovoltaic (PV) market is currently dominated by crystalline silicon (c-Si) technology, which accounts for 95% of the production. However, the record single-junction c-Si solar cell has achieved a record efficiency of 26.81% approaching the theoretical efficiency limit of 29.43%. In an effort to overcome this barrier, multi-junction devices are being investigated, and perovskite/Si tandem technology is attracting a lot of interest. This is because it is compatible with well-established c-Si technology and is comparatively less expensive. Recently, two-terminal (2T) monolithic tandem devices with a c-Si bottom cell and a perovskite top cell have achieved an impressive 33.7% efficiency. By utilizing a solution-based process it allows for fabricating high-quality perovskite layers. However, problems develop when the bottom cell’s light trapping features exceed the thickness of the perovskite layer. To ensure uniform coverage of high-quality perovskite layer, the light trapping features must be lowered to sub-micrometre (< 1 μm) height.

This thesis investigates three methods for creating sub-micron features on the c-Si bottom cell. The first two approaches include wet-chemical processing from the top-down and bottom-up techniques. Using a poly-Si etch solution, the top-down approach aims to lower the height of large surface features from 3-5 μm to less than 1 μm. This method resulted in substantial reflection losses and poor passivation due to surface-induced roughness, even though the peak height was lowered to 0.9 μm. In order to tackle this issue, an additive was added to the mixture, producing a morphology with a 1.1 μm lower peak height, compared to an initial peak height of 3 μm. Further, the passivation has seen a two-fold increase in minority carrier lifetime. This increase is attributed to the reduced surface roughness that was inspected through SEM images. However, the surface still contained nano-scale features whose origination could be related to the cleaning procedure followed or the (i)a-Si:H layer growth. The second method is a bottom-up approach and uses KOH, K2SiO3, and a surface additive to create sub-micron features on a flat Siwafer. Once the chemical concentrationswere optimized, the peak height was effectively lowered to less than 0.8 μm at an F-ratio of F = 2.0. But, this experiment is conducted at a temperature of 80◦ C. Many non-uniformities in pyramid distribution were observed as well as nano-scale roughness for F-ratio of F=0. This seemed to be resolved with better pyramid homogeneity and reduced nano-scale roughness by lowering the temperature to 70◦ C. While, maintaining a peak height below 0.8 μm at F=2.0. Moreover, this approach also exhibited lower reflection losses which is close to reflection observed from large pyramidal features (˜3μm).

The last method includes the use of lithography to produce 2D periodic inverted nano pyramids. This process flow showed that patterns with critical dimensions close to 100 nm may be transferred using high-throughput nano-imprinting lithography. By using a much rigid soft mold that did not showcase any pattern distortion. However, the limitations in mask opening created issues with the nano-pyramid formation. This further requires the optimization of suitable hard mask layers. To sum up, these methods demonstrate the possibility of producing effective sub-micron features, which is promising for perovskite/Si tandem technological advancements.

This study explores the effects and severity of microcracks within Solarge’s innovative lightweight polymer-based photovoltaic modules, aiming to recommend a grading criterion specific to the company’s product range. Unlike the traditional PV modules which predominantly employ a glass and aluminum frame, Solarge utilizes lightweight, fully recyclable polymers. The uniqueness of Solarge’s composition presents a novel landscape in terms of durability and degradation trajectories. A pivotal concern arises from the introduction of microcracks, which inherently diminish a PV module’s power output. Leveraging Solarge’s extensive database of current-voltage measurements and electroluminescence images, an initial analysis discerned the emergence of small diagonal and v-type cracks post-production, predominantly after the lamination process. Subsequent experimental methodologies, encompassing mechanical loading and temperature cycling on these modules, demonstrated the growth of these existing cracks into diverse and more complex formations. This evolution of stressors significantly compromised module performance. A categorization system classifying cracks into noncritical (Category 1), critical (Category 2), and very critical (Category 3) was developed, with associated power losses identified for each. Using linear regression, predictive models for crack progression in each category were established. The study culminated in the formulation of a grading criterion proposed to Solarge, aiming to refine their quality assurance.

Silicon heterojunction (SHJ) solar cell technology is one of the most promising PV technologies because of its high power conversion efficiencies, simple fabrication process and low manufacturing cost. The current world record efficiency of SHJ solar cell reaches up to 26.81%. SHJ solar cell produces the highest VOC over 750 mV among the c-Si solar cell technologies because of the excellent surface passivation provided by the few nanometers (i)a-Si:H layers. The objective of this thesis is to design and optimize the (i)a-Si:H bilayers that not only ensure excellent c-Si surface passivation quality but also allow less-resistive transport of charge carriers in SHJ solar cells.
First, a database focusing on the microstructure properties of (i)a-Si:H layers was established. The database was compiled by systematically varying the PECVD deposition parameters of the pressure, power, and hydrogen dilution ratio. By means of FTIR (Fourier Transform Infrared Spectroscopy) characterizations, higher power and pressure were found to correspond with an increased absorption strength of high stretching modes (HSM), which indicated a higher R* and hydrogen content. These conditions led to the formation of a film that is rich in voids and hydrogen. Conversely, a denser a-Si:H film could be achieved by increasing the hydrogen dilution ratio, where the low stretching modes (LSM) were increased and became dominant. Overall, the built database showcases the possibilities to deposit (i)a-Si:H layers with microstructure factor spanning from 0.193 to 0.805.
Subsequently, passivation optimization of the (i)a-Si:H bilayer on textured (111)-orientated c-Si wafers has been conducted. The optimal passivation is achieved by the combination of a 1 nm underdense i1 layer and a 9 nm dense i2 layer. The void-rich i1 layer with R* = 0.732 and the dense i2 layer with R* = 0.205 improved the passivation greatly from 2 ms to 7.5 ms, as compared to unoptimized STD1 layer (R* = 0.261) and STD2 layer (R* = 0.314). Despite various passivation qualities enabled by various bilayer structures, after hydrogen plasma treatment (HPT), the lifetime of all increased drastically to 17 ms, accompanied by increases FTIR-characterized in both H content and R*, which may indicate that passivation could be saturated after HPT. However, the passivation trend after VHF treatment was not clear. This could potentially be the instability in the PECVD deposition tool.
Finally, (i)a-Si:H bilayers were implemented into FBC-SHJ solar cells, solar cells endowed with a bilayer consisting of X1 layer (R* = 0.382) and D2 layer (R* = 0.205) exhibited an average Voc of 715 mV. Combined with a denser D2 film, RS is reduced, helping to counteract the elevated series resistance associated with the incorporation of the X1 layer, contributing to the enhancement of the fill factor from 78.65% to 80.53%, although at the expense if a slightly lower VOC. The best-performing cell X1 + D2 with treatments gives achieved the highest efficiency of 23.23% (22.33 % on average) and the highest VOC of 717mV compared with an average of 22.24% and 711 mV of the ‘non-optimized’ standard cells fabricated. It is also observed that after treatments, the FF increases while VOC slightly reduces. However, the observed lack of a clear efficiency improvement when using the optimized bilayer as compared to the ‘non-optimized’ standard bilayer could be attributed to the instability of the PECVD tool, which primarily affects the lifetime of precursors, coupled with the relatively large error bars present in the results.

Passivating contacts in the front-rear contacted c-Si solar cells enhances the device performance by quenching the contact recombination and enabling sufficient carrier transport. Tunneling oxide passi- vating contact (TOPCon) which consists of an interfacial oxide and a poly-SiO𝑥 layer is one of the most promising contact techniques in passivating both surfaces of the silicon wafer. However, the full area poly-SiO𝑥 layer is absorptive when it is applied at the front side which has become an efficiency limiting factor. In this project, an advanced local poly-SiO𝑥 passivating contact architecture is proposed and presented. The local poly-SiO𝑥 passivating contacts, so-called “poly-SiO𝑥 finger”, is deposited through a hard mask at predefined locations which will be only placed underneath the metal contacts. The formation of poly-SiO𝑥 finger and its application in the solar cells are discussed.

First, a silicon wafer hard mask is fabricated by a lithography process followed by a KOH wet chemical etch-back process. Specified openings down to 38.7 𝜇m are established which isolate sections of the substrate for the poly-SiO𝑥 finger formation. P+ doped a-SiO𝑥 :H is deposited using PECVD with SiO𝑥 p+ diffused emitter commercial Cz wafers through the hard mask. By investigating the influence of deposition parameters during the PECVD, specifically the power and pressure, decent uniformity of the finger deposition is achieved. An optimized deposition condition of the doped a-SiO𝑥 :H is established for the poly-SiO𝑥 finger formation: an RF power source at 15 Watt, a chamber pressure of 1.5 mbar, and a substrate temperature of 180 °C. A narrow poly-SiO𝑥 finger with a width of 40.0 𝜇m has been demonstrated.

Second, the passivation properties of the symmetrical samples are examined by varying the poly-SiO𝑥 and Al2O3 thickness for the hole carrier selective contacts. A full area p+ TOPCon and Al2O3 symmetric samples were coated on the textured diffused p+ surface with an n-type c-Si substrate to investigate the process parameters on the passivation properties. The optimal 𝑖𝑉𝑜𝑐 of p+ TOPCon samples is 662 𝑚𝑉 and a corresponding 𝐽0 of 156 𝑓 𝐴 𝑐𝑚2 which is obtained with a poly-SiO𝑥 thickness of 50 nm when annealed at 850 °C. The optimal thickness for the Al2O3 passivation layer is achieved by depositing a 20 nm thick layer followed by FGA, with an 𝑖𝑉𝑜𝑐 of 692 𝑚𝑉 and a 𝐽0 of 22.4 𝑓 𝐴/𝑐𝑚2.

Finally, a process flowchart has been created to fabricate c-Si solar cells with the local p+ TOPCon on the front p+ diffused emitter and a full area n+ TOPCon on the rear side. A localized polished area is made by a poly-etch process for the alignment between the substrate and the pattern in the lithography mask. Using the ascertained parameters during the optimization, NAOS-SiO𝑥 combining with 50 nm-thick doped p+ a-SiO𝑥 :H fingers are applied on the p+ diffused surface and 100 nm-thick n+a-SiO𝑥 :H on the rear side. A annealing step is performed for the crystallization. A 20 nm-thick Al2O3 followed by a 75 nm SiN𝑥 layer are deposited on the front side and 100 nm SiN𝑥 layer is applied on the rear side. Lithography, wet chemical etch-back together with Al/Ag(front/rear) evaporation are utilized for solar cells metallization. The fabricated c-Si solar cells with poly-SiO𝑥 fingers has a champion efficiency with an efficiency of 7.91 %, with a 𝑖𝑉𝑜𝑐 of 562 𝑚𝑉, 𝑖𝑛𝑡 𝐽𝑠𝑐 of 34.7 𝑚𝐴 𝑐𝑚2 and fill factor of 40.5 %. The limited performance originates from the poor passivation in the poly-SiO𝑥 local contact area and severe 𝑖𝑉𝑜𝑐 drop after the metallization process. For further improvement, good performing c-Si solar cells by minimizing the recombination in the poly-SiO𝑥 local fingers contacts area and optimizing metallization steps are expected to be fabricated .

This graduation report covers the process and outcome of developing and designing novel photovoltaic (PV) products for architectural and design applications. The project aimed to find innovative solutions for seamlessly integrating photovoltaics into architecture and design and thus contribute to sustainable building practices. With a hands-on, material-driven approach novel PV customization methods were developed and showcased with a demonstrator. Four concepts were proposed based on PV products made with customization methods that were developed during the project. One of these concepts was worked out into a working prototype. This demonstrated the aesthetic qualities of a novel PV coloring technology. The outcome of Solar Style formed the basis of the continued development and commercialization of PV products.

The considerable increase in the number of devices needing connectivity, such as mobile phones and Internet of Things (IoT) devices, has led to an exponential rise in data volumes during the last years, that will surely continue over the next decade. Therefore, it will be increasingly challenging to provide sufficient RF resources. A novel alternative to RF communications is Visible Light Communication (VLC). VLC is a communication technology that uses visible light as an information carrier. The use of VLC for indoor applications has been rapidly growing during the last years – Light Fidelity (LiFi) technology is an example of VLC application – with photodiodes being the most widely used receiving devices. However, looking at both indoor and outdoor communication, photovoltaic (PV) cells represent a relevant alternative for detecting the information. One of the advantages of using a PV cell as receiver is the huge sensitive area for detection of the information that simplifies alignment between transmitter and receiver.

Different light sources can be used in VLC. Typically, either LEDs or LASERs are considered, depending on the characteristics of the link (such as distance, type of receiver, indoor/outdoor application). These light sources differ in terms of spectrum, directionality, optical power density and bandwidth. The performance of the whole VLC link strongly depends on the characteristics of the light source, since it affects the ability of the receiver, such as a PV-device, to detect the information when it overlaps with the ambient light, that can reach very high values, especially in outdoor applications where the ambient light is the sunlight. Therefore, the modelling and analysis of the performance of different light sources in a PV-based VLC link will pave the way towards the realisation of a PV-based communication system of the future; and it is the focus of this thesis project.

The project goals were achieved by first reviewing the characteristics of light sources, to understand their advantages and drawbacks in (PV-based) VLC. This was followed by the development of models of the VLC data-link, with a focus on the light source, which took into account various factors such as the type of light source, its location relative to the receiver, and its dynamic behaviour. This was followed by the realisation of a test setup, to characterise different light sources, and the models were then used to simulate the light distribution from the actual light sources. Finally, the framework was used to simulate a LED-based solar simulator and an outdoor VLC data-link.

The overdependence on the tradition energy source have caused a serious of ecologi-cal problems such as the increasing emission of carbon dioxide. To combat this and achieve carbon neutrality, attention has shifted towards sustainable energy, particu-larly wind, tidal, and solar energy. The solar cell catches significant interest due to its ability to directly convert solar energy into electricity through the photovoltaic (PV) effect. The silicon heterojunction (SHJ) cells got a lot of attention with high efficiency and simple fabrication process. The record efficiency of SHJ solar cell is 26.81% from Longi [1]. The fabrication process for SHJ solar cells involves the use of plasma en-hanced chemical vapor deposition (PECVD). However, the use of toxic and flammable gases in the doping process poses safety risks in laboratories. The parasitic absorption introduced by a doped layer, leads to drawbacks in solar cell performance. Conse-quently, alternative materials like dopant-free carrier selective contacts (CSCs), divided into hole transport layers (HTL) and electron transport layers (ETL), have attracted con-siderable interest. Transition metal oxides (TMO) and metal fluorides stand out in do-pant-free material research.
This study investigates three metal fluorides (LiF, MgFX, and SrFX) as ETL in SHJ solar cells. Initially, four plasma treatments (PTP, PT, PTB, and noPT) are examined as inter-face treatments in combination with LiF as ETL in SHJ solar cells. Results indicate that PTP is the most compatible with LiF, yielding the highest efficiency. Additionally, stud-ying the impact of LiF thickness on cell performance reveals that a 1 nm thickness shows higher Voc and FF, resulting in higher efficiency. Further exploration into the deposition order of transparent conductive oxide (TCO) and LiF highlights that depos-iting LiF on the rear side preserves passivation properties, ensuring device perfor-mance. Investigations into metal electrode contacts on the rear side reveal that a sput-tered Ti/Ag contact with LiF provides the best performance due to its no-venting dep-osition process. On the front side, copper plating proves superior to screen printing due to better-controlled grids and a less aggressive process, benefiting cell perfor-mance.
We expand the optimal parameters obtained from previous experiments to MgFX and SrFX. We explore the thickness influence on cell performance. The optimal thickness of MgFX and SrFX are 1 nm and 4 nm, respectively. Finally, SHJ solar cells integrated with MoOX as HTL and LiF, MgFX, and SrFX as ETL show significant improvement in light response within the 300-600 nm wavelength range. The combination of MgFX/MoOX yields the highest efficiency, with the champion device exhibiting 716 mV of Voc, 38.02 mA/cm2 of Jsc, 76% of FF, and 20.69% efficiency, surpassing reported efficiencies within the same cell structure.

Silicon heterojunction (SHJ) solar cells are one of the most promising PV technologies nowadays due to high photoconversion efficiencies and low manufacturing costs. However, standard front/back-contacted (FBC) solar cells feature a front metal grid that brings shading to the front side of the devices, which limits the conversion efficiency of solar cells. One solution is to move metal contacts fully to the back by introducing interdigitated-back-contacted (IBC) architecture. In 2018, IBC-SHJ solar cells achieved a photoconversion efficiency of 26.7% holding a record for single-junction c-Si cells. However, the standard fabrication process of IBC solar cells comes with increased complexity and manufacturing costs. The focus of this research is on developing and optimizing a simple and industry-appealing fabrication process for high-efficiency IBC-SHJ solar cells.

The first part of the project investigates the simple processing of IBC-SHJ solar cells featuring tunneling recombination junction (TRJ). The first tunneling IBC devices are fabricated successfully. However, shunting is observed from the J-V curves of fabricated devices, which can be related to the internal shunting of tunneling IBC architecture and high lateral conductivity of p-type nc-Si:H-based blanket layer. Hence, alternative contact stacks are designed for application in the previously developed flowchart with the aim to minimize the lateral conductivity of the blanket layer and keep the fabrication process simple.

The proposed hole collection contact stack is firstly implemented in the front junction (FJ) FBC solar cells. The FJ FBC devices reach Voc of 704 mV and FF of 79.29% . Rear junction (RJ) FBC solar cells are fabricated featuring a novel electron collection contact stack that is developed within this thesis. Voc of 715 mV and FF of 82.24% are obtained in RJ devices. The results of RJ FBC solar cells with a newly developed contact stack show excellent results in terms of FF, making it a promising candidate for further application in IBC devices. The introduction of the optimized device design enabled the successful fabrication of IBC solar cells with the simple process developed for tunneling IBC devices while ensuring no shunting occurs. Fabricated devices represent a proof-of-concept of the novel configuration, providing a promising starting point for future development.

Silicon solar cells account for about 95% of the total photovoltaic market share. Poly-Si passivating contacts are promising techniques enabling high performance c-Si solar cells with conversion efficiency over 26.0%. The highly absorptive nature of poly-Si materials makes the transparent passivating contacts attractive, such as poly-Si(O_x). However, the research of p⁺ poly-Si(O_x) passivating contacts on a textured surface with an in-situ doping nature is still missing. Therefore, in this thesis, the optimization of p⁺ poly-Si(O_x) carrier selective passivating contacts on double side textured wafers are given and the application in solar cells is demonstrated.
Firstly, the influences of different interfacial tunnelling oxides fabrication methods, nitric acid oxidation of silicon (NAOS-SiO_x), plasma assisted N₂O oxidation (PANO-SiO_x), and thermal oxidation (t-SiO_x) on the passivation of p⁺ poly-Si(O_x) passivating contacts are explored. It is found that Si⁴⁺ stoichiometry in the tunnelling oxide layer is an indicator for its quality. There is a positive correlation between Si⁴⁺ and SiO_x density. The t-SiO_x can be denser with higher Si⁴⁺ compared to its counterparts NAOS-SiO_x and PANO-SiO_x. And fewer boron dopants in-diffuse phenomenon can be observed in the t-SiO_x samples. Then, different intrinsic layer deposition approaches are explored. The intrinsic layer deposited by LPCVD results in higher iV_oc compared to PECVD counterpart. The enhanced iV_oc is given by suppressing the blistering which is caused by hydrogen accumulation at the interface between intrinsic layer and SiO_x. It is assumed that less hydrogen accumulation exists in intrinsic layer deposited by LPCVD. Next, p⁺ doping layer thickness is changed from 0 nm to 200 nm to observe its effect on the passivation quality. The optimum p⁺ doping layer thickness is found to be 100 nm with the highest iV_oc. After that, the hydrogenation process is introduced to enhance chemical passivation by coating SiN_x:H and performing forming gas annealing. The highest iV_oc with the standard hydrogenation process is 674 mV. In order to improve the hydrogen level of p⁺ poly-Si(O_x) passivating contacts, AlO_x:H inserted layer is used for the hydrogen reservoir together with SiN_x:H. It results in an improved iV_oc of 685 mV. It is assumed that the hydrogen in AlO_x:H diffuses into c-Si/p⁺ poly-Si(O_x) interface and enhances the chemical passivation.

Besides, metallization methods of p⁺ poly-Si(O_x) passivity contacts are also studied. There are two approaches to complete the metallization process. Firstly, with thin p⁺ poly-Si(O_x) passivating contacts, TCO is required to provide with the lateral and vertical carrier transport as respect to the carrier collection. However, it commonly brings with the TCO introduced sputtering damage. The iV_oc losses are 70-90 mV when TCO is sputtered on p⁺ poly-Si(O_x) passivating contacts. When the thickness of p⁺ doping layer is over 50 nm, sufficient lateral conductivity can be provided with thick p⁺ poly-Si(O_x) passivating contacts. Therefore, it can directly contact with metal which is the second method of metallization. However, when utilizing this metallization method, the metal induced recombinations need to be taken into consideration when contacting with p⁺ poly-Si(O_x) passivating contacts. Thus, the plot of J_o,total along with different metal fractions is fitted to extract J_o,metal of p⁺ poly-Si(O_x) passivating contacts with 100 nm p⁺ doping layer. When contacting with evaporated aluminum, the measured J_o,metal is around 91 fA/cm². In addition, after calculating, there is 24 mV iV_oc loss when p⁺ poly-Si(O_x) passivating contacts contacting with metal. It is smaller than the loss induced by TCO sputtering. Therefore, the thick p⁺ poly-Si(O_x) passivating contacts with 100 nm p⁺ doping layer directly contacting with metal is used as metallization method for the application in c-Si solar cell. In addition, after linear fitting and calculating, ρ_c between p⁺ poly-Si(O_x) passivating contacts with 100 nm boron doped layer and c-Si is about 23 mΩ· cm².

Finally, p⁺ poly-Si(O_x) passivating contact is applied in c-Si solar cells together with n⁺ poly-Si(O_x) passivating contact as front surface field. The poly-poly solar cell of the highest quality has the following electrical performance: V_oc is 648 mV, J_sc is 35.9 mA/cm², FF is 73.1% and η is 17.0%. A roadmap to realize 22% is given by addressing the bottlenecks of poly-Si(O_x) passivating contacts based c-Si solar cells.

Photovoltaic technology has become one of the leading renewable alternatives for energy production. One main factor in the diminished performance of a photovoltaic module is partial shading, due to the resulting mismatch conditions in the module. However, it is difficult to understand how a specific PV module reacts to shading in comparison with others, as currently the ability of a module to withstand shading is usually expressed in vague qualitative terms on its datasheet. In this work, the development of a shading tolerability calculator in MATLAB was completed. This tool can relatively easily and quickly calculate the shading tolerability of a module as a numeric parameter (ST), which can then be used for characterization and comparison purposes.

First a MATLAB based model to simulate the IV characteristics of a PV module under different conditions (including partial shading) was developed. The model was developed at a cell level, and was translated to a module level by taking the series connection of cells into account, and modeling the impacts of reverse bias and bypass diodes operation. Validation with experimental data showed errors at Pmpp remained below 4.5%.

Next, the shading scenarios to be considered were defined and developed. The objective was to determine Pmpp of a given PV module under all possible shading scenarios, using the IV simulation model developed. The possible shading scenarios were based on a PV module split into 12 equal sections, and considering two irradiance levels: 100 W/m2 for shaded sections, and 1000 W/m2 for unshaded. To improve the speed of the model, which was an important aim within this project, the existence of equivalent scenarios based on the symmetry of the module was utilised. The Pmpp value was only simulated once for every unique scenario, greatly reducing the required number of simulations and simulation time.

Based on the above, the development of a calculator for the shading tolerability parameter of a PV module was accomplished. The ST values for more than 40 PV modules were calculated, giving ST% values ranging between 22% and 29%. Correlations between different module parameters were explored to see their impact on ST. One main result seen was the impact of bypass diodes on ST, specifically the considerable positive effect of a higher number of bypass diodes. Another was the positive correlation between temperature coefficient of open circuit voltage and ST.

Finally, a case study for the calculation of ST for a half-cell butterfly module was implemented. This involved modeling parallel connections in PV modules, as well as updating the IV simulation model to include this new type of PV module configuration. The ST values for two half-cell butterfly modules were calculated, giving ST% values of around 42%. This was significantly higher than those calculated for the conventional modules, highlighting the improved shading tolerance of half-cell butterfly modules. The adaptability of this model to be able to calculate the shading tolerability of any type of configuration of PV module was also demonstrated through this case study, paving the way for future research.

In recent decades, there has been increasing concern about the impact of climate change on the earth. Various countries are actively developing sustainable energy technologies, of which solar cell is one of the new energy sources with the most attention. This thesis is based on poly−Si(O_x) cells consisting of SiO_x/poly−Si(O_x) passivating contact. Various methods have been investigated to mitigate the TCO (IWO) deposition induced passivation degradation and to optimize the screen printing process.

First, approaches to reduce the passivation degradation due to IWO deposition were explored. The power density and working pressure in IWO deposition were optimized. With utilizing 1.23 W/cm² power density and 5×10⁻³ mbar working pressure, the 𝑖𝑉_𝑂𝐶 degradation was reduced to 4.7 mV for 𝑛⁺ sample (NAOS-SiO_x) and to 7.9 mV for 𝑝⁺ sample after deposition of 75 nm IWO. Besides, hydrogenated amorphous silicon and AZO were used as buffer layers for the 𝑝⁺ SiO_x/poly−Si(O_x) samples, finding that they were effective in reducing sputtering damage. Then, the optimal post-annealing condition was investigated, which turned out to be vacuum annealing at 400 ^◦𝐶 for 30 min, recovering the 49 mV and 60 mV 𝑖𝑉_𝑂𝐶 for 𝑛⁺ sample (thermal-SiO_x) and 𝑝⁺ sample, respectively. Based on the above experiments, the first cells were prepared with a maximum efficiency of 17.4%.

Second, the existing screen printing process in the lab was optimized. The 0.37% organic solvent was added into the silver paste, reducing the viscosity of paste. The snap-off distance was changed to 0.02 mm in order to improve the continuity of printed grids. Moreover, the squeegee speed was optimized to 30 mm/s, limiting the spreading of silver paste to 57.3 𝜇m, much narrower than the initial spreading distance of 155.3 𝜇m.

Finally, a batch of poly−Si(O_x) cells were prepared by applying the above various optimized conditions. The cell with optimized IWO and optimized screen printing process performed best with an champion efficiency of 18.9%.

Crystalline silicon (c-Si) homojunction architectures like aluminum back-surface field (Al-BSF) and passivated emitter and rear cell (PERC) dominated the solar cell market for the last decades. Recently, carrier-selective passivating contact (CSPC) designs have shown that they can effectively reduce recombination losses and exhibit efficiencies above 25 % which approaches the Shockley-Queisser limit of single-junction solar cells. To overcome this intrinsic efficiency limit, research and industry have started to investigate multijunction devices which utilize two different absorber layers in order to reduce the spectral mismatch losses. In this project, the focus lies on the fabrication of a high temperature CSPC bottom cell with polycrystalline silicon oxide (poly-SiOx) for the application in a 2-terminal perovskite/c-Si tandem device. Poly-SiOx features a higher transparency due to a wider band gap which can decrease the free-carrier absorption (FCA) and induce larger band bending in comparison to the classic polycrystalline silicon (poly-Si) contacts.
To fabricate a c-Si solar cell with high temperature carrier-selective passivating contacts, the passivation of the contacts was optimised using symmetric lifetime samples. It was found that the optimal processing conditions for the dry thermal oxidation process and the high temperature annealing step are 675 °C for 3 minutes and 900 °C for 15 minutes, respectively. This resulted in an implied open-circuit voltage (iV_OC) for the n-doped and p-doped symmetric samples after hydrogenation of 745 mV and 674 mV, respectively. Those optimised processing conditions were adopted for the fabrication of a single-junction n-type front-side polished and p-type rear-side textured CSPC solar cell. This resulted in a solar cell with an efficiency of 16.67 %. By lowering the thermal budget of the recovery annealing conditions after the sputtering of the transparent conductive oxide (TCO), the passivation properties are restored more effectively. This resulted in an enhanced solar cell with a final efficiency of 18.76 %. Other techniques to improve the performance like the modification of the p-layer thickness, the incorporation of an additional annealing step after the a-Si deposition, or the introduction of indium tungsten oxide (IWO) as the TCO did not result in an improvement of the final solar cell efficiency. Optical simulations were performed in GenPro4 to investigate the optical performance of the solar cell. Finally, a 2-terminal perovskite/c-Si tandem device with a high temperature carrier-selective passivating c-Si bottom cell was fabricated in cooperation with TU Eindhoven. The final tandem solar cell exhibits an efficiency of 23.10 % with a fill factor of 74.00 %, a V_OC of 1.76 V and a J_SC of 17.81 mA/cm².

In the Netherlands, like in several other countries, there is a need to increase the contribution of Solar Energy to the energy generation technologies portfolio. To fully achieve integration and to use the entire potential of photovoltaic energy, certain levels of public knowledge and acceptance of the technology must be reached. In this context the role of scientific websites and information sources on Solar Energy gains importance significantly.

In this paper the development of a new improved version of the Dutch PV Portal (DPVP), a website on photovoltaic energy on Netherlands territory developed by the Photovoltaic Materials and Devices (PVMD) research group of TU Delft, is developed. After a prelaminar website quality assessment to establish the preferred areas of improvement and overall quality status, a set of improvement objectives were defined. These included: i) Integration of real-time real life performance data of a case study in the DPVP, ii) creation of a shading function using LiDAR data, iii) Improvements of the mathematical model, iiii) Creation of a real-time alarm for performance sensitive parameters.
These features are developed in the form of a case study monitoring platform which is integrated in the website. To do this a set of alarm systems as swell as visual monitoring tools were developed.

Furthermore, with the use of the newly integrated data and existing weather databases, an accuracy analysis of the DPVP model is performed. Thanks to this, accuracy and limitation of the website’s mathematical model is assessed, and areas for future improvements are identified.