In this thesis, two new types of crystalline silicon texturization were developed, eventually aimed to be used in a triple junction solar cell from monocrystalline silicon and two thin film silicon alloy layers. The bottom of the two thin film silicon layers is made of hydrogenated nanocrystalline silicon (nc-Si:H). The current problem with this technology is that the adhesion of the nc-Si:H to a flat surface of crystalline silicon is not always ideal. This can be improved by texturing the monocrystalline silicon. This also improves the optical efficiency. The standard pyramidal texture method of crystalline silicon has proven to be too sharp which leads to cracks in the layer of nc-Si:H during deposition. The two investigated texturing methods are a periodic hexagonal texture with semispherical walls created using photolithography and a random texture of craters using a sacrificial layer of polycrystalline silicon. For the hexagonal texture, a photolithography process was designed and tested on the ability to grow crack-free nc-Si:H. It was found that a texture period of 3 µm was most suited for the desired nc-Si:H layer thickness of 3-3.5 µm. For the sacrificial layer process, the effect of the different parameters on the crater size was investigated. These tests showed that an amorphous silicon (a-Si) layer thickness of 1-2 µm gives the largest craters. The ideal implantation energy is dependent on both the implanted ion and the a-Si layer thickness. It was also found that the crater size increases with increasing dopant concentration. An anneal temperature of 950 °C for 60 minutes was determined to result in the largest craters. Furthermore, argon implantation using an energy of 250 keV in 1 or 2 µm of a-Si showed the biggest promise in terms of crater size, with an average hole diameter of around 320 nm. In terms of optical performance, the hexagonal texture results in a slightly lower mean reflectance over a wavelength range of 300 to 1200 nm. The angular distribution of the reflectance showed that the reflectance of the hexagonal texture was very dependent on the measured angle and this angular dependence varies for different wavelengths. This indicates good light scattering of this texture. The results for the large craters show light scattering at approximately the same level as the photolithography samples, but more gradual over different angles. The best hexagonal and sacrificial layer textures were used to create SHJ's. Unfortunately, the minority charge carrier lifetime measurements of these SHJ's showed that the deposited passivation layers were likely to be too thin, which resulted in very low lifetimes. Consequently, the efficiency of the sacrificial layer SHJ's was only 0.1%. The efficiency of the hexagonal texture SHJ's were much higher, at 10.0%. Still, this efficiency was lower than anticipated. The reflectance measurements of these solar cells showed that the average reflectance of the SHJ's using the photolithography texture was 13.4% with TCO. This is lower than the reflectance of the sacrificial layer SHJ, which was at 14.4% with TCO.

Photovoltaic systems play a crucial role in the shift from conventional energy sources to renewable energy alternatives . Considering the sudden boom in PV systems, several IT firms invested heavily in the creation of online PV system sizing tools for customers worldwide. This was done to ease the calculation process of sizing a Solar System. However, a deep study and analysis of the various available system sizing tools in the market proved that none of the tools independently satisfied all the constraints. Some tools could be used specifically for economic feasibility analysis, while others could be used for just dimensioning purposes. There was always a shortcoming in every software tool. Hence, there raised a need to come up with a dedicated tool that could satisfy all the constraints. This thesis aims to develop one such tool which could incorporate certain proven modelling techniques in order to provide optimistic results. At first, accurate solar insolation data is obtained for the purpose of initial DC side energy yield calculation of the PV system. Succeeding this, chosen transposition and thermal models are used for the calculation of optimal tilt and optimal azimuth of the PV Modules. In addition. the battery is sized and the charge controller is modelled. Subsequently, a comparative study between Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT) techniques of charge controllers which gives insight on the pros and cons of using each type of charge controller technology is performed. In addition, system sizing of a Solar-Diesel Hybrid System is done followed by an economic analysis which includes the calculation of Total Cost of Ownership (TCO) and Payback Time. Finally, the system sizing was validated with an actual test system which gives insight into the practical differences between the site conditions and the theoretical conditions.

Semiconductor lifetime and power density are considered to be two important development directions of power converter design in the future. Especially in some high dynamic application, the operation condition is changing frequently causing the temperature swing of semiconductor, and it leads to thermal expansion and contraction which affects the lifetime or reliability of semiconductor. A high maximum temperature or a large temperature swing leads to short lifetime. Meanwhile, high power density is a general trend. If the size of a whole system is limited, a high power density converter enables more functionality of the system. Also, high power density also leads to high portability. Works have been done to use interleaved and high switching frequency converter to get a high power density. However, those converters such as interleaved buck converter do not help to improve semiconductor reliability because it can only operate in synchronous conduction mode (SCM) and triangular current mode (TCM).

In this work, a $20kW$ DC/DC converter for highly dynamic application is designed. The four-switch buck-boost converter is chosen because of its flexibility and its possibility to get longer semiconductor lifetime and higher power density. It is possible to offer a free-wheeling interval in which no voltage is applied on the inductor, the transferred power can be regulated by adjusting the duty cycle of this interval. In addition, an optimal modulation scheme is proposed for this topology which further helps improve the reliability of semiconductor. An optimal power stage design is given which is a two-stage interleaved structure. Plus, a close-loop control strategy is given according to the design.

The proposed modulation scheme is tested with a low voltage level prototype, and the performance prediction is verified.

[Background] This project provides a proof of principle to use microneedles in combination with optical spectroscopy for bilirubin detection. For newborns, high bilirubin levels in the blood can lead to serious health consequences, such as jaundice, which can lead to brain damage. Therefore, it should be detected as early as possible. However, bilirubin monitoring of newborns in remote African areas is insufficient. In these areas the current invasive methods are time-consuming, and minimally invasive methods, such as bilirubinometers, are quite expensive, and may be inaccurate in babies with stronger skin pigmentation. In short, the conditions are not optimal to detect jaundice, and therefore an affordable method is needed to accurately and quickly measure the concentration of bilirubin. [Aim] The aim of this project was to develop microneedles for optical spectroscopy, and to test them in simulated skin to determine the usability for reflection measurements. [Fabrication] Microneedles are created by using microfabrication techniques with a focus on backside exposure. Multiple prototypes have been developed and evaluated based on dimensional properties. The prototype closest to the requirements was chosen to take measurements. These were the microneedles with an average length of 410 μm, an average base diameter of 106 μm and an average tip diameter of 43 μm. [Measurements] To test the microneedles for their performance, an indentation test, and transmission and reflection measurements has been performed. The indentation test showed that the average fracture point of one microneedle is at a force of 72.5 mN and an average displacement of 63 µm. The fracture point per area microneedle is on average 16.5 N/mm^2. Furthermore, transmission measurements have shown that the reduction in transmission is 70 % from the base and 75 % from the tip. Therefore, the maximum amount of light that can be used for reflection measurements is 7.5 %. Moreover, reflection measurements have shown that the differences in color concentrations in the simulated skin results in differences in absorption and therefore reflection values. Also, the measurements in simulated bilirubin (skin simulation with yellow colorant) showed a dip in the blue spectrum, e.g. at 460 nm, the absorption peak of bilirubin. [Conclusion] In this project microneedles have been developed that are minimally invasive, biocompatible, optically transparent, and easy-to-process. The first measurements have shown that it seems possible to use the microneedles in combination with optical spectroscopy to detect differences in “bilirubin” concentrations. Moreover, the microneedles can be used to puncture the skin without fracturing. However, the actual usability in the clinical setting still needs to be investigated. Other important recommendations for future research are research into measurements with real bilirubin; the optimal alignment between the microneedles and the optical spectrometer; optimization in the manufacturing process to cover the spaces between the microneedles; and possible other development methods for microneedles (e.g. 3D printing) and other designs (e.g. mirrors for efficient light use).

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

F2R is a generic IC fabrication based platform that allows for the fabrication of miniature and flexible sensing functionalities for minimally invasive medical instruments. Examples of these minimally invasive medical instruments are catheters and guidewires. By introducing more materials to the F2R technology, it can be extended to more applications. An example of such an application is neural brain probes. This thesis focuses on the introduction of parylene and platinum to the F2R technology. This is a challenging task, as many different technologies have to be introduced and modified. Therefore, the main objective of this thesis was to develop a fabrication process that allows for the electrical and mechanical evaluation of flexible parylene-platinum based electrodes and interconnects. In order to electrically and mechanically evaluate the devices, test structures were designed. These test structures make the electrical and mechanical evaluation possible and can be used for further evaluation of future developments. Furthermore, several fabrication technology modules have been developed. The effect of particles on the stability of the device has been reduced by investigating their origin. The step coverage of platinum was improved by optimizing the dry etching of parylene. This was done by introducing CF4 to the etching process, which resulted in a desired 45° slope of sidewall of the parylene structures. Also, the patterning of platinum was improved by separating the etching process into two steps. This resulted in fenceless and clean metallization. Since the adhesion of the layers is of major importance for in-body applications, the adhesion of parylene and platinum was investigated. By exploring several adhesion promoting techniques, the overall adhesion of the devices was found to be good, and therefore sufficient for electrochemical characterization. All the previous technology modules were integrated where possible, and have led to the fabrication of flexible parylene-platinum based devices. These test devices consist of a silicon island with bond pads and flexible part with electrodes and a comb-meander structure. Rolling tests have shown that the devices can be rolled to an inner diameter of <1 mm without damaging the interconnects. This flexibility is required for the assembling of a 3D brain probe using a flexible microelectrode array.