Dublin City University. School of Mechanical and Manufacturing Engineering
Abstract
In order to increase the efficiency of solar cell modules it is necessary to make the optimum use of light incident upon them. Much research has been conducted to improve light absorption through front surface texturing and light trapping schemes. Laser light is commonly used in industry for various applications including marking and texturing. By controlling laser parameters, it is possible to tailor macro and micro structures in most materials. A CO2 laser operating at 10.6ΞΌm wavelength was used to produce grooved textures in fused quartz material with a view to its usage as a cover glass on top of the photovoltaic cell surface. With correct texturing it is postulated that increased energy absorption can be promoted due to trapping of light within the photovoltaic cell due to total internal reflection and enhanced optical path lengths. Analysis of the effects of the laser parameters on the texture geometry and surface morphology was performed through a combination of cross-sectioning and scanning electron microscopy. Transmission spectra through the textured glass samples were recorded, and transmission through the glass was improved for most samples after acid etching. It was found that for acute angles of incidence of wavelengths of natural sunlight upon the cells, greater coupling efficiencies were achieved compared to flat surfaces, due to the increased light trapping effect. The main contributions of this work include examination and quantification that indicate the laser textured solar superstrates can increase the light trapping effect within silicon solar cells and that an enhanced light trapping can be achieved when silicon quantum dots deposited directly on a textured superstrate. Another two important contributions are found in the development of characterisation methods and analyses of microstructures relevant to light trapping in current and emerging solar cell technologies. These include the design, fabrication, development, and verification of a newly designed and commissioned depth-from-focus based optical profilometer with which new results in the metrology of translucent surfaces with micro-scale roughness are presented. Software to analyse serial FIB-SEM sections of monolithic porous microstructures was also developed. The results gained from these characterisation methods have allowed, and it is postulated will in the future provide, a more detailed understanding of the light trapping process with various microstructures
