The growing need to reuse plastic waste has increased interest in recycled polymers for structural and semi- structural applications. Recycled polypropylene (rPP), when combined with glass fiber reinforcement and processed via 3D printing, presents a promising route for reducing plastic waste while enabling the fabrication of load-bearing components. However, the long-term durability and environmental resistance of 3D-printed rPP reinforced with glass fibers (rPP-G) remain insufficiently understood. This study investigates the degradation behavior of 3D-printed rPP-G under combined ultraviolet (UV) radiation, elevated temperature (60 and 80 °C), and high humidity (up to 95% Relative Humidity).
Results show that under moderate aging (60 °C), rPP-G retains relatively stable tensile properties with only minor reductions in strength and stiffness. In contrast, more severe aging at 80 °C and 95% RH results in notable deterioration, including approximately a 6% decrease in ultimate tensile strength, a 2% reduction in Young’s modulus, and a 30% decline in storage modulus compared to unaged material. Additionally, a shift in glass transition temperature toward lower values suggests increased molecular mobility and reduced stiffness. Creep performance is significantly affected under severe conditions, with a substantial reduction in time to failure (up to 522.58% reduction compared to the unaged specimen), indicating compromised long-term load-bearing capability.
SEM analysis reveals increased fiber pull-out and interfacial debonding, while ATR-FTIR confirms oxidative degradation. Humidity is identified as the dominant degradation factor, with temperature acting as a key accelerator. These findings highlight both the potential and limitations of rPP-G for outdoor structural applications. ... Read more

Perovskite Light-Emitting Diodes (PeLEDs) represent a highly promising LED technology due to their exceptional color purity, tunable emission color, and low manufacturing cost. However, the current record external quantum efficiency (EQE) for PeLEDs is limited to 32\%, still below the 40\% achieved by organic LEDs (OLEDs). This limitation primarily stems from defects within the perovskite layer and at interfaces between different layers in the device. Effective passivation of these defects is essential for further advancing PeLED efficiency.

In this thesis, we established the first operational PeLEDs within the PVMD group, leveraging its perovskite solar cell production line. We developed the fabrication process from the ground up and characterized the resulting device performance.

The first part of this thesis addresses the stability of perovskite layers during optical testing in ambient air. We observed that carrier lifetime measurements depend heavily on the perovskite's exposure time to air and the presence of protective overlayers, rather than solely on its inherent optoelectronic properties. This instability arises from rapid perovskite degradation in air. To mitigate this, we employed spin coating to deposit a protective PMMA layer over the perovskite and optimized this coating process. Characterization confirmed that PMMA significantly slows degradation. Additionally, we identified and corrected alignment issues in the photoluminescence quantum yield (PLQY) measurement setup, which had introduced substantial uncertainty. We refined the PLQY testing procedure to enhance result reliability.

The second part focuses on developing a quasi-2D perovskite emissive layer (EML) with low bulk defect and superior optical properties. Based on quasi-2D perovskites (PEA2(FAPbBr3)n−1PbBr4) typically exhibit better emission characteristics than bulk counterpart (FAPbBr3) We first confirmed the phase composition of our synthesized perovskite, verifying the formation of quasi-2D perovskite with the targeted phase distribution (n = 3). We then introduced two additives: [2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2PACz) and KBr to enhance the optoelectronic property of EML. Photoluminescence (PL) testing revealed that 2PACz significantly enhances PL intensity, while KBr showed no such effect. Subsequently, we applied different antisolvents to improve perovskite film morphology. Results demonstrated that ethyl acetate yielded the highest PLQY. Our champion quasi-2D perovskite sample achieved a PLQY of up to 49\%.

The third part details the development and characterization of carrier transport layers for PeLEDs. For the electron transport layer (ETL), we employed 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) and used simulations to study how its thickness affects optical performance. Simulations indicated negligible performance variation for TPBi thicknesses between 40 nm and 80 nm. For the hole transport layer (HTL), we fabricated a self-assembled monolayer (SAM) HTL using [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic Acid (MeO-2PACz) and [4-(3,6-Dimethoxy-9H-carbazol-9-yl)butyl]phosphonic Acid (MeO-4PACz), which could reduce interfacial defect at HTL/ETL interface. However, devices with this SAM-HTL structure didn't emit light during voltage sweeps and exhibiting low turn-on voltages in J-V characteristic. We attribute this to electrical breakdown caused by electron tunneling through the extremely thin (1-2 nm) SAM layer. To suppress tunneling, we introduced an underlying NiO$_{x}$ layer. This modified structure demonstrated to be successfully prevented tunneling and enabled functional PeLEDs. To further optimize hole transport while minimizing thickness, we modeled the relationship between HTL thickness and electron tunneling probability. Calculations revealed that increasing the HTL thickness by approximately 3 nm effectively shields against tunneling. This optimized, ultra-thin HTL design paves the way for PeLEDs operating at low voltages with state-of-the-art optical performance. ... Read more

Radioisotope thermoelectric generators produce electricity for space exploration. These generators use thermoelectric material, usually a silicon-germanium alloy, to turn heat from radioactive decay into electricity. Recently, the thermoelectric performance (ZT) of Si80Ge20 was improved by reducing the grain size to the nanometer range, significantly lowering the thermal conductivity.
To optimize the properties of silicon-germanium we studied the effect of doping concentration and processing parameters on the microstructure and properties of boron-doped Si80Ge20 produced by arc melting, ball milling and spark plasma sintering. The thermal conductivity was estimated with a model. The electrical conductivity and Seebeck coefficient were measured.
Some conclusions from this work are that the current production process can be used to produce nanostructured Si80Ge20Bx with a crystallite size of 50-100 nm. This material reaches a maximum, but not necessarily optimal, doping concentration when x=1 due to limited solubility. The material suffers from grain growth when exposed to high temperatures for several days. The use of iron in the ball milling process significantly affected the microstructure and properties. ... Read more

Advanced High Strength Steels (AHSS) are essential to reduce weight and consequently CO2 emissions in the automotive industry. However, they are vulnerable to Hydrogen Embrittlement (HE), because many strengtheningmechanisms present in their microstructures are also a cause of HE. The contributions of individual microstructural features to HE is not yet completely understood. Several challenges occur when studying HE in these steels. Firstly, since all strengthening mechanisms interact with hydrogen, isolating the effect of singular features is complicated. Moreover, HE is a time-sensitive phenomenon which requires experimental setups that minimise time between hydrogen charging, testing and measuring in order to avoid desorption between steps. Two types of iso-parametric microstructures were created for this project, in order to isolate the effect of individual features. Firstly, ferritic steels containing either Vanadium Carbide (VC) or Titanium Carbide (TiC) nano-precipitates of different size distributions since the addition of nano-precipitates is a promising candidate to provide both strength and
ductility. Secondly, Dual Phase (DP) steels with varying amounts ofmartensite in a ferrite content, since these steels are the most widely used in the automotive sector.

This research begins by subjecting nano-precipitate strengthened steels to annealing treatments designed to achieve two distinct precipitate size distributions. A 2 hour heat treatment leads to precipitates of around 10 nm in size, that grow to more than 10 nm after 20 hours. Heat treatments are performed in either N2 or H2 gas in order to provide both a reference steel as well as one that charges the precipitates with hydrogen. After hydrogen contents were measured using Thermal Desorption Spectroscopy (TDS), the hydrogen gas is found to predominantly charge large incoherent precipitates with hydrogen.
These precipitates of sizes larger than 100 nm are present in themicrostructure from the steelmaking process. Smaller (semi-)coherent carbides with sizes on the order of 10 nmare not observed to contain hydrogen after the treatment. Hydrogen trapped in incoherent precipitates is trapped irreversibly in carbon vacancies inside the precipitate bulk, meaning that it does not diffuse throughout the steel. The activation energies could only be determined for TiC precipitates, which range from69 kJ/mol to 115 kJ/mol. This type of trapping inhibits accumulation of hydrogen at critical areas such as crack tips, which means that no HE is observed in these specimens. Secondary Ion Mass Spectrometry was performed to visualise hydrogen trapped in the incoherent precipitates. Hydrogen in the TiC precipitates is primarily stored at the interface with the matrix, whereas in VC
precipitates it is distributed throughout the entire bulk. This is explained as an effect of a higher C-vacancy concentration in VC..... ... Read more

H igh-temperature (HT) oxidation plays a significant role in various stages of the steelmaking process, including hot rolling. When exposed to high temperatures and oxygen partial pressure, the steel composition near the surface can be altered as alloying elements deplete. Additionally, the characteristics of the oxide scale, such as thickness and phase composition, vary depending on the oxidation conditions. Due to the experimental challenges of studying such rapid processes under extreme conditions, predictive models are necessary to estimate the substrate surface and oxide scale composition as well as the general oxidation rate of the alloy.... ... Read more

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

Quantum computing has gained a lot of interest from researchers and industry due to its great potential to solve some complex problems in various fields. One of the biggest challenges is developing hardware suitable for the extremely low operation temperatures required by quantum computers. Specifically, the wiring material of a quantum computer must provide good electrical conductivity while keeping the thermal load to a minimum. Delft Circuits’ cryogenic flexible cable design made from metalized Polyimide (PI) with Silver (Ag) thin films as conductors offers a promising solution for quantum computer i/o systems. This thesis aims to investigate the effect of fabrication and design parameters on the electrical and thermal properties of silver thin films, utilizing the Residual Resistivity Ratio (RRR) as an indicator to assess the thermal load of cryogenic flexible cables. The RRR is calculated by taking the ratio of electrical resistivity measured at room temperature and extremely low temperatures of liquid He (4.2 K). The key parameters for the experimental investigation include oven heat treatment, lamination, silver purity, film thickness, aging and storage. The RRR behavior of samples with varying fabrication and design characteristics is explored through cryogenic measurements. Subsequently, the RRR results are analyzed and supported by material characterization via SEM and XRD. The results show that heat treatment results in higher RRR values due to grain growth and lower grain boundary density, leading to lower electrical resistivity at low temperatures. Heat treatment parameters including temperature, pressure, duration, ambiance, and cooling rate play a significant role in the resulting microstructure of the silver film, and consequently, in their RRR values. Furthermore, the study reveals that the lower purity level leads to decreased RRR values of the silver film due to higher electron scattering caused by impurities. A linear relationship is found between the film thickness and the RRR behavior of silver thin films. Lastly, aging and storage do not result in a significant change in the RRR values of heat-treated silver thin films. This thesis provides a deeper understanding on the influence of fabrication and design parameters on the low-temperature resistivity of silver thin films. It highlights the key role of these parameters in tailoring the microstructure of silver thin films to achieve desired material properties. ... Read more

Large-scale hydrogen storage is a crucial part of the energy transition. The usage of salt caverns has a great potential in this process, but there are open questions regarding the construction’s lifetime which need to be investigated prior to their implementation. In this work, potential construction steels were studied. The conditions in a salt cavern were imitated on laboratory scale with an experimental high-pressure setup. Two steels, J55 and H2-ready X56, were systematically exposed to pressure/temperature cycles, gas (H2 and N2), water and brine. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques were used for the characterisation of the steels’ surface, focussing on corrosion effects and crack formation. For both steels, a significant impact of moisture and salt ions could be shown. However, only for J55, intensification of corrosion and cracking on the surface due to hydrogen gas exposure was found. Pronounced crack formation over the entire surface of J55 was revealed. For X56 significantly less crack formation could be observed. Overall, the results strongly indicate better resistance of X56 than J55 against the conditions in a salt cavern, used for hydrogen storage. ... Read more

High entropy alloys (HEAs) are new potential materials for hydrogen storage applications which could help with the transition towards sustainable energy sources. The rate of hydrogen kinetics is one of the material properties that is important for the storage and other hydrogen related applications. One of the limiting factors on the rate of hydrogen kinetics is hydrogen diffusivity. Thus far, there has been no reports on hydrogen diffusivity for HEAs in relation to hydrogenation kinetics.

Therefore, this project investigates hydrogen diffusivity in equimolar TiVZrHfNb and the influence of hydrogen concentration on hydrogen diffusivity to gain better understanding of hydrogenation kinetics. The selected HEA has been found to absorb the highest amount of hydrogen (2.5 H/M) among other HEAs.



The investigation was done by a computational approach using ab initio molecular dynamics. BCC and face-centered cubic (FCC) supercells with different hydrogen concentrations (H/M = 0.2, 0.8, 1.4, 2, 2.4) were simulated at a temperature range of 773 – 973 K. At the same time, experimental electrochemical hydrogen charging using chronoamperometry and cyclic voltammetry was performed in order to compare computational and experimental values of hydrogen diffusivity.



The electrochemical hydrogen charging did not result in hydrogen absorption, most probably due to the passivation of the sample surface.

From the simulation results, the values of activation energy and pre-exponential factor were estimated to be in the range of 0.26 – 0.48 eV and 0.73 – 2.95 x 10-7 m2/s, respectively. Hydrogen diffusivity was found to be higher in BCC than in FCC. In BCC the hydrogen diffusivity slowly decreases linearly with increasing H/M. In the case of FCC, the hydrogen diffusivity was found to be the highest at 2.4 H/M while at 2 H/M the diffusivity was the lowest. The analysis of hydrogen occupation at 2 H/M shows that most of the hydrogen atoms are trapped inside tetrahedral sites. It is possible that the hydrogen occupation in the tetrahedral sites results in the optimum hydrogen distribution where the repulsive interaction between hydrogen atoms is the lowest. At concentrations above 2 H/M, an additional repulsive force between hydrogen atoms seems to contribute to the increase of hydrogen diffusivity. ... Read more

Hydrogen has been contemplated as a desirable energy source of the future with enormous possibilities to create a carbon-neutral society. Since palladium (Pd) readily absorbs hydrogen even at low pressure and room temperature, Pd and its alloys are suitable for hydrogen production, purification, storage, gas sensors, and fuel cell catalyst. However, primary requirements for industrial applications are not always satisfied, such as usability under operation conditions, minimum capital cost, and sustained hydrogen embrittlement. Therefore, developing stable Pd-based thin films to investigate correlations between microstructural features and mechanical properties of a material is of great importance for many hydrogen-related technologies.
In this thesis particular interest has been focused on the stability of a series of magnetron sputtered Pd thin films of different nanostructures i.e., non-voided compact and nano-voided open columnar morphology. The X-ray diffraction (XRD) analysis methods are advanced, utilizing the tailored microstructures of the Pd films suitable to investigate the interplay between microstructure and hydrogenation properties of Pd-based thin films. Interpretation of the stress state and microstructural changes during hydrogen cycling are studied utilizing XRD line-profile analysis and the deformation mechanisms are systematically discussed. The change in dislocation density by the generation and annihilation of dislocations at interfaces reflects the difference in film-substrate interaction. The insertion of an intermediate layer between the Pd film and a rigid substrate can prevent buckle-delamination that is caused by the large volume expansion due to hydrogen absorption but it also changes the hydrogen absorption performance. The different effects on the absorption properties in the case of compliant (polyimide) and rigid (titanium) intermediate layers are illustrated. The results of this work showed that the strong clamping usually suppresses or reduces hydrogen absorption, whereas, the flexible layer enhances the lifetime of Pd thin films when exposed to prolonged hydrogen during cycling. The research in this thesis deepens the understanding about an appropriate combination of film microstructure and choice of the intermediate layer to strengthen Pd-based thin films.
... Read more

Silicon heterojunction (SHJ) solar cells have exhibited efficiencies well above 25%. To further boost the efficiencies of c-Si-based solar cells, high-bandgap perovskite cells are stacked on top achieving a record efficiency of 29.52%. However, as most of the high-quality perovskite films are solution-processed, the front surface of the bottom device should be flat. Therefore, in this work SHJ bottom c-Si cells featuring front-side-flat and rear-side-textured morphology, which delivers high V_OC together with excellent near-infrared response, have been optimized as bottom cells for tandem configurations.

Firstly, RF-PECVD deposition conditions of a (i)a-Si: H monolayer for symmetric <100> flat c-Si surfaces were optimized. The optimized (i)a-Si:H monolayer ( 10-nm-thick) was obtained using pure SiH₄, which results in rather moderate passivation performances (teff = 1.2ms, i-V_OC = 701 mV).
To improve further the passivation quality of monolayer (i)a-Si:H on flat <100> surface, other passivation approaches aiming at incorporating more H without promoting detrimental epitaxial growth have been investigated.
With a bilayer deposition approach, which features firstly a less H-containing (i)a-Si:H to prevent epitaxial growth and then a second H-rich (i)a-Si:H layer, the passivation properties were slightly enhanced to τeff=1.4 ms and i-V_OC=704 mV. Subsequently, by combining the bilayer approach with a post HPT, τeff of 2.0
ms and an i-V_OC of 714 mV were achieved. Finally, by combining the bilayer approach with an intermediate HPT, the optimal passivation sample was deposited, with τeff of 2.4 ms and an i-V_OC of 720 mV on the flat <100> surface.
To gain a better understanding of the correlation between passivation qualities and the microstructure properties of (i)a-Si:H on flat <100> surface, the layers have been characterized mainly via Fourier-transform infrared spectroscopy (FTIR). From the analysis, it can be concluded that the passivation layer that contains
sufficient H and a higher fraction of monohydrides is beneficial for achieving a better passivation quality.

For the two-terminal tandem solar cells, bottom cells with (n)-contact on top are preferred due to the optical advantage of the perovskite top cells with the p-i-n configuration. Therefore, a first tandem cell with (n)a-Si:H has been fabricated in collaboration with TU Eindhoven resulting in 22.2% efficiency. Starting from
this first fabricated tandem cell, its main optical limitations have been identified by performing advanced optical simulations using GenPro4, and the main strategies to overcome these optical drawbacks have been defined. By optimizing the front anti-reflection layers (MgF₂ and ITO) thicknesses (at 100 nm and 20 nm, respectively), and reducing C₆₀ thickness from 20 to 10 nm, front reflections, and parasitic absorption can be minimized. Thus a gain of implied photocurrent density of 1.8 mA/cm² for the tandem cell was obtained.
Further, by implementing (n)nc-SiOx:H doped layer in the SHJ bottom cell, instead of standard (n)a-Si:H layer the reflection between the top and bottom cell is also reduced, and enhanced light incorporation into the bottom cell is obtained. By adopting all the above optimizations and also adjusting the perovskite
layer from 473 nm to 530 nm, a total improvement of 2.7 mA/cm² in implied photocurrent density with respect to the initial 22.2% tandem cell can be achieved.
After having identified different optically optimized SHJ bottom cells for tandem applications, both rear junction and front junction single-side-textured SHJ solar cells were fabricated. Firstly, the passivation quality of (i)a-Si:H/(n)-layer and (i)a-Si:H/(p)-layer on different (i)a-Si:H were investigated. Then RJ solar cells
with three different (n)-type layers [(n)nc-SiOx:H;(n)nc-Si:H;(n)a-Si:H)] have been fabricated with optimal thicknesses individuated from the tandem optical simulations. Furthermore, a tunnel recombination junction SHJ solar cell with a layer stack of (n)nc-Si:H/(p)nc-SiOx:H/(p)nc-Si:H has been fabricated and measured as well.

In conclusion, various doped contacts (both n- and p-type) were successfully implemented into SHJ solar cells, which delivered V_OCs range from 700 to 714 mV and FFs range from 77.8% to 80.9%. Therefore, different well-functioning SHJ solar cells have been developed and are ready to be implemented as bottom cells for high-efficiency tandem devices. ... Read more

In this work, mechanical stability and kinetics of hydrogen (de)sorption of thin Palladium films (100 nm) magnetron sputter deposited on a magnetron sputtered Titanium intermediate layer were studied. In particular of two film morphologies, an open voided columnar morphology and a compact columnar morphology, the substrate-induced stress and its relaxation upon hydride formation were investigated at room temperature. By conducting in-situ X-ray diffraction (XRD) measurements combined with line-broadening analysis of the diffraction profiles, it was observed that the α (H-poor phase) to β (H-rich phase) transition induces stress that could (partially) relax by dislocation generation. After several absorption-desorption cycles (at 0.05 atm p(H2)), however, this stress increase prevents a full transformation to the β phase. When applying a higher partial pressure p(H2) = 0.1 atm for both of the selected open and compact-structured Pd/Ti thin films, a full phase transformation was observed. The corresponding phase transition kinetics, stress states and microstructural behaviors of the open and compact-structured Pd/Ti samples were found to be different. The microstructural changes and the kinetics of phase transformation during H2 (de)sorption are explained in terms of stress development and its relaxation through dislocation/defect generation. ... Read more

The global production of steel in a year is in the range of several millions of tonnes due to its essential function in industries such as automotive, manufacturing, and construction among others. However, a major challenge faced by the steel industry in the development of new steel grades is the inability to predict surface behaviour, such as the concentration profiles of alloying elements like manganese. This is due to the inability to predict the oxidation behaviour during the processing of steel. In order to solve this challenge, experimental data regarding oxidation on a short timescale is required which is not yet well-addressed in literature. Some of this data required will be generated in this research project via the experimental investigation of the oxidation of Fe-Mn binary alloys at high temperature. In this project, the oxidation experiments are performed on Fe-Mn alloys having a manganese composition ranging from 0.5-7% Mn in temperatures ranging from 1000-1150 degrees Celsius and oxygen partial pressures ranging from 0.1-0.3 atm. The oxidation behaviour is studied using thermogravimetric analysis and the oxide layer is then characterised using X-ray diffraction. The in-situ evolution of oxide structure is observed using high temperature X-ray diffraction, and finally the rate determining mechanism for the oxidation of Fe-Mn alloys at high temperature is identified. ... Read more

Surface compositions play a predominant role in the efficiency and lifetime of membranes and catalysts. The surface composition can change during operation due to segregation, thus controlling and predicting the surface composition is essential. Computational modelling can aid in predicting the alloy's stability, along with designing surface alloys and near-surface alloys which can outperform existing catalysts. A computational model to predict surface segregation in ternary alloys is developed. The model is based on Miedema's semi-empirical model that is used to predict mixing enthalpies. The segregation enthalpy is parameterized to describe pairwise interactions between nearest-neighbours and then used in Monte Carlo simulations. Monte Carlo simulations enable to predict short-range ordering in the surface and subsurfaces; both affect the performance of a material as a catalyst. The computational model obtained in this work is able to screen through a vast range of alloy compositions and can qualitatively predict the alloy's stability in a gas environment. In this thesis the model is applied to design a novel ternary Pd-based material for membranes that can be used to separate hydrogen from a gas mixture. Addition of specific amounts of Cu and Zr to Pd results in a material with reduced H2S poisoning as compared to a pure Pd surface as well as an enhanced permeability. The computational model obtained in this work allows to systematically assess the composition of ternary surface alloys and near-surface alloys and is a large improvement over the trial and error approaches currently used. ... Read more

Environmental factors in the field cause partial shading of Cu(In,Ga)Se2 (CIGS) thin-film photovoltaic modules. Partial shading forces shaded cells into reverse bias leading to irreversible efficiency loss. The origin of the irreversible efficiency loss is the formation of defects in the shaded cell. The defects are going by the name of ’worm-like defects’. Understanding the mechanisms involved during the formation of worm-like defects can result in preventive measures to mitigate negative effects of partial shading.

The formation of worm-like defects involves a moving hot-spot across the cell. The exact mechanisms involved in the movement of a hot-spot is unknown. The problem in studying the mechanisms present in these hot-spots is an unknown current density and temperature. After rapid formation of worm-like defects severe changes in the solar cell are observed.

This work expands the knowledge on changes in geometry, composition and crystal structure after worm-like defect formation. X-ray diffraction results shows crystal structure of CIGS below worm-like defects has not changed. Energy dispersive X-ray results showCu rich areas near the back contact and areaswith high Ga and O content near the transparent conductive oxide. A band outside the worm-like defects is observed where Se is exchanged with S while Cu, In or Ga is exchanged with Cd.

Furthermore, a new experimental method is presented that allows control over locally applied conditions. The new method shows applied conditions can be controlled inducing features while resistive heating is suppressed.This enables future research on involved mechanisms.

Based on experimental results multiple possible mechanisms are proposed. In the authors view a plausible and major mechanism is electromigration of Cu towards the back contact. This migration is enhanced by the electromagnetic field and elevated temperature. Cu migration initiates a phase transformation of CIGS into a Cu rich and Cu poor phase. Subsequent to this phase transformation is a reaction of Ga and O. Further testing with this method is needed to investigate in which order mechanisms occur during worm-like defect formation. ... Read more

Alkaline water electrolysis will become increasingly important for supplying the world with sufficient renewable energy, and with raw material for the chemical and pharmaceutical industry. Zero Emission Fuels B.V. (ZEF), a technology start-up based in the Netherlands, is developing a small scale alkaline electrolysis cell (AEC), which is integrated in a methanol producing micro-plant. The challenge of this project is to look into the use of polymers for the encapsulation of the ZEF AEC. The conditions of the ZEF AEC are not to be neglected. The system will run in a 30wt% KOH solution at a temperature of 90 °C and a pressure of 50 bar. Not many polymers will be able to withstand these conditions for a desired lifetime of 20 years. Using CES EduPack, a selection of 30 potentially suitable polymers has been made, from which high density polyethylene (HDPE), 40% glass-reinforced polyphenylene sulfide (PPS-40%gf) and polysulfone (PSU) are further investigated. Based on a literature review and a simple KOH ageing test, HDPE is found unsuitable for application in the ZEF AEC. PPS-40%gf and PSU have been subjected to durability testing for a range of different conditions involving a variety of KOH concentrations (15, 30 and 45wt%), and two oxygen partial pressures (O2 at 5 bar and air with pO2=20%) at different temperatures (90, 120 and 170 °C). The purpose of the ageing experiments is to give a better understanding of the effect of these parameters on the structure and integrity of the polymer; and to eventually be able to acquire a lifetime prediction. Extensive characterisation of the exposed samples has been carried out using different techniques, including weight measurement, tensile testing, DMA, creep-recovery testing, DSC, FTIR, XRD and SEM. After 12 weeks of ageing, it is found that glass-filled polymers are unsuitable for application in a strong alkaline solution at elevated temperatures, due to the dissolution of the glass fibres, which leads to a reduction in mechanical and barrier properties. However, the PPS matrix and PSU are found to be resistant to thermo-oxidative and chemical degradation in the tested ageing conditions. Only subtle changes in mechanical, visco-elastic and thermal behaviour are observed, which can be assigned to the effects of physical ageing. Due to the undesirable brittle nature of PPS, it can be concluded that PSU is the most promising candidate for the long-term application in alkaline electrolysis. ... Read more

The so-called “hydrogen economy” became one of the scientific targets among the different renewable energies alternatives, as a result of the efforts to transition from fossil fuels to environmentally-friendly energy sources. In this context, various options to transport and store hydrogen are being explored. Gaztransport & Technigaz (GTT) company, intending to be part of this challenge, is exploring the possibility to transport liquid hydrogen (LH2) in pre-existent ship’s containers initially designed for liquid natural gas (LNG) transportation. This project is about the study of the surface effect of the interaction between hydrogen with iron-based alloys in the case of 304L stainless steel (uncoated and coated with TiO2) and Invar alloy.The methodology consisted of electrochemical induced hydrogen evolution on an iron-based austenitic metal cathode taking advantage of the intermediate adsorbates (atomic hydrogen) generated during the reaction to study the electrochemical adsorption efficiency. Characterisation of the materials, by techniques like XRF, XRD, optical microscopy, and SEM, is conducted before and after hydrogen exposureso that it was possible to evaluate the effect of hydrogen ingress.The results showed that the chemistry of the surfaces is irreversible changed after the electrochemical induced hydrogen sorption/desorption process due to the formation of oxides. The amounts of hydrogen desorbed were quantified after different H2 loading times. In all cases, the amount of hydrogen desorbed showed a maximum after which the hydrogen desorbed decreased significantly. The maximum for uncoated 304L stainless steel was after 24 h, 90 min for the coated 304L, and 2 hfor Invar. The welds are the most vulnerable sections to hydrogen ingress in both cases. XRD results before hydrogen exposure revealed that 304L consists of an austenitic matrix with around 5% of ferrite. An increment of the austenitic volume fraction of 2.2% was observed after the H2 sorption/desorption process. Invar is a purely austenitic phase, and no changes in the phase composition were observed after the H2 sorption/desorption process. ... Read more

Because of its extraordinary material properties, like its high melting point and thermal stress resistance, low erosion and swelling rate, and high radiation damage resistance, highly deformed pure tungsten has been chosen as the plasma facing surface material for the ITER reactor divertor. The study of tungsten’s recrystallization behavior and damage response during operation conditions is thus important because the divertor will have to withstand high heat fluxes and temperatures during service which induce recrystallization. This phenomena alters the microstructure of the material, inducing degradation in its properties, like loss in mechanical strength and embrittlement making it prone to large plastic deformation, surface roughening, crack networks formation and propagation. Understanding this behavior under the ITER reactor operation circumstances is paramount for the success of the reactor.

The aim of this project was to test regimes simulating steady state operation and high frequency and temperature transient pulses called ELMs (Edge Localized Modes) striking the divertor. Recent research has shown that the degradation and behavior of tungsten under these transient conditions does not consistently follow the expected parameters characterized in the literature. According to it, recrystallization, grain growth, and crack formation seem to be suppressed by the plasma loading under these regimes, thus a new understanding of the material behavior for these circumstances must be developed. To do this, ITER grade tungsten samples were subjected to a hydrogen plasma beam at DIFFER’s Magnum-PSI with temperatures at the strike point ranging from ~1000 to ~1500 °C and high frequency pulses that increased the surface temperature by ~200 to ~300 °C above the steady state temperature. The surface thermal shock response to the plasma pulses was characterized by means of infrared and pyrometer readings at the samples’ surface during exposure. Temperature and power density calculations were correlated with identified damage morphologies on the targets and a damage map for the experiments was elaborated, which showed that the most severe damage (cracks and crack networks) begin to appear in the range of the measured recrystallization temperature of the samples, which was lower than expected.

Using Vickers hardness, the recovery and recrystallization kinetics of the material were characterized by means of logarithmic decay and a modified version of JMAK recrystallization kinetics that includes an incubation time for the onset of recrystallization. Recrystallization kinetics were found to accelerate as the hydrogen exposure progresses, thus yielding lower effective activation energies for recrystallization when comparing furnace one hour exposures, plasma one hour exposures, and plasma four hour exposures. This pointed to the presence of hydrogen actively reducing the activation energy for self-diffusion. Simulations of hydrogen diffusion were performed to test this hypothesis, and even though the total concentration is low, given that the high experimental temperature does not permit trapping of the hydrogen, the diffusing atoms may still play a role in accelerating the recrystallization kinetics.

Based on the results of this research, it is proposed that interstitially diffusing hydrogen segregating to voids or grain boundaries is modifying the behavior of surrounding tungsten crystal lattice. Specifically, the mobility of the grain boundaries may be increasing because the hydrogen’s presence would be promoting the creation of ledges in the grain boundary resulting in an overall free energy reduction for grain boundary diffusion. This localized defect formation would require a lower concentration of hydrogen than that required for solute drag or other suppression mechanisms, and might be mechanism behind the behavior observed in this work’s experiments. ... Read more

Within the photovoltaic industry, a lot of research is done in order to minimize losses which are created during the conversion of solar light to electrical energy. In a crystalline silicon solar cell light has to pass through several layers before it enters the silicon wafer where the electron-hole pairs are generated. As one can imagine, if more light reaches the active layer, more electron-hole pairs can be generated. It is highly desired that only one layer, the active layer, is absorbing photons of the solar spectrum. The active layers at the sunny side of the silicon wafer should be highly transparent for solar light. In addition to being transparent, these layers should be conductive to extract the generated charge carriers to the metal contacts. Current layers applied at the sunny side are not optimally transparent, so it is still possible to increase the efficiencies in the crystalline silicon solar cells. In this study, doped silicon oxide layers have been explored as a potential more transparent layer for passivation of both the silicon surface and the metal contacts. Two routes for the fabrication of doped silicon oxide layers were investigated: post-oxidation of doped polycrystalline silicon layers and post-doping of in-situ grown silicon oxide layers. To characterize this new type of material, several different measurement techniques have been applied to improve our understanding of Low-Pressure Chemical Vapor Deposition deposited silicon oxide passivating contact layers. It was found that the structure and composition of the layers is very different for these different routes. However, very good and stable surface passivation (minority carrier lifetime of >3ms) can be achieved with both types of silicon oxide layers. Also, sheet resistance measurements have indicated that phosphorus doping in silicon oxides is possible. For better insight into the electrical properties of these layers, further testing in electronic test structures is advised. ... Read more

The Pd-based metal membranes have been focused on many studies, because they are the most promising candidates for hydrogen separation. If Pd-based membranes are designed in nanoscale, then the introduced high volume fraction of grain boundaries can act as fast diffusion paths for hydrogen atoms that leading to an increase of hydrogen separation rate. However, due to the substantial amounts of grain boundaries, the nanocrystalline material tends to show a rapid grain growth at operating temperature (that leading to the coarse grains), which may lead to the failure of this membrane in further applications. However, grain growth could be effectively inhibited by thermodynamic stabilization method-that is solute segregation to grain boundary region. In this thesis, a thermodynamic grain boundary segregation model is developed and is applied to many types of metallic binary alloys, including the Pd-Cu, Pd-Zr, Pd-Y, Fe-Zr, Y-Fe and so on. From this model, the segregation tendency of alloying constituents is determined, and the solute concentration in grain boundary is obtained. Moreover, the grain boundary energy (GB) of investigated alloys can be calculated via this model, by comparing the calculated GB energy with that of pure Pd, we are able to determine whether these alloys can be stabilized by the segregation-introduced thermodynamic stabilization. These calculated results have been compared with those reported in the literature, verifying the predictability of this model. In addition, X-ray diffraction (XRD) analysis, including the XRD residual stress measurement and X-ray peak broadening analysis have been performed on both Pd_0.7Cu_0.3 and pure Pd thin films, the experimental results will help us determine whether the solute segregation occurs and whether this alloy can be stabilized by the solute segregation. ... Read more