A Study of Femtosecond Laser Processed Microtextures on Silicon Wafers to Enhance Optical Absorption

Silicon wafer-based solar cells require texturing of the front surface to absorb most of the incident light falling on it. Texturing also increases the front surface area leading to increased charge recombination, and surface damage due to oxidation, making the process counterproductive. In this work, the surface of silicon wafers is textured with a femtosecond pulsed laser to generate a wide variety of surface structures. Variation in size and shape of these surface structures with laser parameters and their effect on reflectance is studied. Optimal textures for solar cell applications were identified by analyzing reflectance, increased front surface area, and surface oxidation. The fabricated textures consisted of periodic structures such as cones and hemispheres with sizes between 800 nm to 15 μ m. Besides, a transition from 3D to 2D structures was observed with variation in laser power and scanning speed. Among the different structures, hemispheres of radius 2 μ m were found to be the most optimal ones based on reflectance and surface damage. However, the lowest value of reflectance was observed for conical-shaped structures, which was as low as 5% without using an anti-reflective coating. The study suggests that optimization of textured surfaces on silicon wafers is crucial in enhancing the performance of solar cells.