Abstract

Energy is the number one problem facing humanity today. Solar cells can capture and transform clean and abundant solar energy into electricity. However, their efficiency must increase and their material and fabrication costs must decrease in order for them to be considered as a viable alternative to the fossil fuels. This research explores and studies new methods for fabricating silicon micro- and nano-scale structures in an economical way as building blocks for crystalline silicon solar cells to lower their overall manufacturing cost while increasing their overall efficiency.
A novel cost-effective approach was proposed and studied for texturing the crystalline silicon using the gas lift effect (GLE). The new proposed method takes advantage of the generated bubbles to create a gas lift effect that increases the surface wetability and removes undesired gas bubbles during the texturing process. This technique requires 50% less chemicals and 60% shorter etching time to achieve the same reflectivity.
Modeling and simulation techniques were used to investigate and elucidate the fluid flow patterns inside the silicon texturing system operating under the new GLE approach. The simulation tool validated the correlation of the lower fluid velocity with the reduced surface coverage, uniformity and subsequently less optimal surface reflectivity. Various inlet designs were modeled and evaluated using a simulation tool for optimal performance. The best inlet design was fabricated and tested resulting in the validation of the simulation work and significant improvement in the GLE texturing system performance.
Two solar cell devices, one based on the novel GLE texturing approach, and the other based on the conventional method, were designed, fabricated and characterized. The application of the new GLE texturing approach resulted in considerable improvements in overall power efficiency of silicon solar cells without any additional increase to the production cost.
Micro and nano structures can enhance optical absorption characteristics and help with providing a more direct path for charge transport to the contacts resulting in an increased overall efficiency. An array of silicon micro-rods with nano-tip was fabricated through a novel low cost multistage approach. The transformation of the pyramid-covered silicon surface to the array of free-standing micro-rods with nano-tip as well as their growth mechanism was investigated. At lower than 80% pyramid coverage, the number of nanostructures dropped dramatically and no nano-structures were obtained at low surface coverage values of less than 50%.
Transparent conductive films (TCFs) can be a viable low-cost alternative to the expensive Indium Tin Oxide (ITO) used in solar cells. A novel thermoplastic nanocomposite of copper nanowires and polymethylmethacrylate was developed by solution mixing technique. Thin films of highly conductive nanocomposites were fabricated by solution casting. This investigation demonstrated that the addition of electric conductive nanoscale fibers to a polymer solution at low concentration levels can transform the plastic to highly conductive phase while maintaining an acceptable transparency of about 55%.