Abstract

Increase in the global demand for energy, has put a lot of pressure on natural resources such as gas and oil that are predicted to be diminished in not too distant future. Global warming which is the consequence of burning fossil fuels is an alarming issue as well. Solar cells that can transform the clean and abundant solar energy into electricity have shown to be one of the promising solutions for supplying the energy demand which is the number one problem that we face today. However, efficiency along with costs associated with the material and fabrication of solar cells should be improved in order to make them a practical alternative to the fossil fuels. Silicon (Si) has proven to be the most dominant semiconductor used in optoelectronic devices. It is the second abundant element on the earth, which results in its lower production costs compared to other semiconductors. Furthermore, based on Shockley–Queisser limit calculations, maximum efficiency of a single junction solar cell occurs with a band gap of 1.34eV therefore, Si having a band gap of 1.12eV is highly recommended to produce maximum efficiency of a solar cell. Since solar technology is still not cost-effective and efficient enough to compete with the fossil fuels, researchers are investigating new methods to overcome the mentioned limitations.
In this work, multicrystalline silicon (mc-Si) which is less expensive compared to the single crystalline silicon (sc-Si), is textured with nanosecond laser; not only to decrease the optical loses due to reflection from the surface but also to increase the absorption by increasing the optical path length of the light. Texturing was performed on the mc-Si surface and the effect of laser fluence, spot overlap percentage, and number of scans on the Solar Weighted Reflectance (SWR) as well as surface morphology of mc-Si was studied. Statistical analysis was implemented to identify the most efficient laser parameters to reduce SWR and it was found that increase in average surface roughness (Ra) and depth decreases the SWR. Ra and depth were measured by means of scanning electron microscopy and optical interferometry.
The experiments were done both in ambient air as well in acetone confinement and a comparison was made in terms of Ra, depth and SWR. The technique of acetone-assisted laser texturing takes the advantage of bubble formation, which results in a debris free microfabrication where depth and consequently SWR is improved. Results validated the correlation of the higher number of pulses with the increased depth and Ra when texturing was conducted in acetone.
In order to understand if depth or Ra plays the major role in SWR reduction, a regression analysis was performed, and the results indicated that the increase in depth plays more significant role in reduction of SWR compared to increase in Ra. Finally, an attempt was made to fabricate the P-N junction and the electrodes with both textured and untextured mc-Si wafer surfaces. From the I-V characterization of these devices, it was seen that untextured wafer as well as wafers textured at 0% overlap produced output power.
Solutions are presented to improve the electrical properties of the fabricated cells that might be implemented in the future works.