Silicon carbide (SiC) and silicon oxide (SiOx) have garnered increased attention to reduce the parasitic absorption at the p layer when compared to p-aSi.An outstanding question is how the integration of p-SiC and p-SiOx impacts the metastability of the solr cells. Previous work in the PVMD group at TU Delft has studied the stability of the p-nc-SiOx in detail revealing from experimental results that stable efficiency remains elusive.
This thesis investigates the impact of p-a-SiC on the light-induced degradation (LID) of p-i-n solar cells, aiming to compare its degradation performance with that of p-nc-SiOx. Prior to comparison, p-a-SiC fabrication via plasma-enhanced chemical vapor deposition (PECVD) is extensively explored, as it serves as a widely used light absorber in thin-film silicon solar cells. Various parameters such as power pressure and gas flow rate of the source gas for silicon carbide formation are meticulously studied to achieve optimal P-a-SiC performance. Once the optimal fabrication conditions are identified, light absorption experiments are conducted and characterized using JV and EQE measurements to assess LID performance.

The characteristic feature of ”thin” film solar cells is that they are thin, ranging over thicknesses of a few micrometers. This results in a drop in the light trapping capability of the solar cell, owing to the Beer-Lambert law. Thus, there is a need to optimize light management to enhance the amount of light being trapped in the photoactive region. This can be done by imparting texture in the glass superstrate to scatter the light and thereby allowing the light to travel over a longer distance in the absorber.

In this thesis, the focus is mainly on developing a high-quality reproducable procedure for achieving periodic texturing in glass and understanding the enhancement in the optical impact of the surface. the first objective was to understand the influence of the different processes involved in the fabrication procedure of periodic textured glass superstrates. This was done by varying the parameters associated with the individual processes and observing the resultant impact on the deterministic characteristics of the texturing process. The influence of the mask design, employed in the photolithography process, on the dimensionality of the texture was also analyzed. Based on the aforementioned results, an optimized recipe was developed and successfully implemented to enhance the depth of the periodic hexagonal texturing imparted onto the glass. Additionally, an indicative parameter Re/P was developed to imply the effect the processes had on the quality of the texturing.

This project also ventured into studying the growth of nanocrystalline silicon on the deep textures developed using the optimized recipe. Following this, an extensive optical analysis of the honeycomb textured superstrates was carried out to realize the scattering effect induced by this texturing on interacting with light. This was done by studying the transmittance components and the angular intensity distribution of the periodic textured glass. The interaction mechanism of the textures was found to be dependent on the wavelength and
the size of the textures. In general, there was a linear increase in the diffuse transmittance with texture height, for all wavelengths of light. However, it was noticed that the slope of this relationship varied for the different wavelengths, since it was mainly dominated by different scattering mechanisms for different wavelengths. Finally, the influence of the optical impact of these hexagonal textures on solar cell performance was also studied by studying the Jsc of the micromorph tandem solar cells, developed on deep hexagonal textures of different periodicities.

Thin-film silicon photovoltaic (PV) technology has an enormous potential in the solar power market due to its light weight, flexibility and ease of integration. This enables it to have a wide range of applications like roof top and building integrated installations making it more sustainable. Some of the other key benefits of thin-film silicon PV technology include energy efficient production, less material usage, low temperature coefficient and low manufacturing cost. The relatively low conversion efficiency, however, is the major drawback of thin film silicon solar cells. Hydrogenated amorphous silicon (a-Si:H) grown by plasma-enhanced chemical vapor deposition (PECVD) is one of the extensively employed light absorbers in thin-film silicon solar cells. However, light-induced degradation (LID) of a-Si:H is one of the biggest limiting factors of this technology. LID is a metastable defect creation phenomenon that decreases the conversion efficiency of the a-Si:H solar cell after prolonged exposure to light. This is known as the Staebler-Wronski effect (SWE). SWE has been a subject of research over the past 4 decades. Despite tremendous efforts, the complete suppression of the LID has not been demonstrated yet. Nevertheless, there has been a great progress in characterisation of the defect creation and also the optimisation of solar cells to minimise the effect of LID.
In this thesis, LID of three single junction a-Si:H thin film solar cells with different qualities of a-Si:H absorber layer namely high bandgap a-Si:H, low bandgap a-Si:H and high/low bandgap a-Si:H are studied. Light soaking experiments were carried out for several hundred hours and the performance of the solar cells was analysed through external quantum efficiency (EQE) and illuminated JV characterisations at regular time intervals. Some of the key findings of the experiments include severe LID of high bandgap a-Si:H absorber layer due to increased defect creation, enhanced recombination at the p/i interface in all of the devices and also a significant relationship between the performance and light soaking temperature. Furthermore, the thermal annealing study revealed that, maximum recovery of the performance parameters can be observed at an annealing temperature of 180 ^◦C.
Based on the findings of the above mentioned study, additional experiments were carried out to investigate the stability of the devices with different materials as a buffer layer at the p/i interface. The results of the experiments revealed the significance of the buffer layer in the performance of the devices and also its influence on the LID. In addition, the analysis suggests that intrinsic silicon oxide (i-SiO_X), intrinsic hydrogenated amorphous silicon (i-a-Si:H), and p-doped hydrogenated amorphous silicon (p-aSi:H) are some of the potential candidates for a buffer layer in an a-Si:H solar cell that could give an improved stabilised performance. Furthermore, the speculation of light induced boron diffusion into
the a-Si:H bulk through the buffer layer was tested by another light soaking study to investigate effects of window layer (p) doping on LID. The study found no correlation between the window layer doping and the p/i interface degradation indicating the possibility of a different defect creation mechanism responsible for the enhanced recombination at the p/i interface.